CI: Add l2tp to test
    
    Sample run
    
    ```
    ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
    
    ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
    ::   Test
    ::   Test
    ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
    
    ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
    
    :: [ 15:21:16 ] :: [   LOG    ] :: ip l2tp tests
    :: [ 15:21:16 ] :: [   LOG    ] :: ip l2tp tests
    :: [ 15:21:16 ] :: [  BEGIN   ] :: Running '/usr/bin/python3 /usr/bin/ip-l2tp-tests.py'
    test_add_l2tp_add_tunnel (__main__.IPL2tpTests) ... Tunnel 3000, encap UDP
      From 192.168.11.12 to 192.168.11.13
      Peer tunnel 4000
      UDP source / dest ports: 5000/6000
      UDP checksum: disabled
    ok
    test_add_l2tp_add_tunnel_session (__main__.IPL2tpTests) ... Tunnel 3000, encap UDP
      From 192.168.11.12 to 192.168.11.13
      Peer tunnel 4000
      UDP source / dest ports: 5000/6000
      UDP checksum: disabled
    Session 1000 in tunnel 3000
      Peer session 2000, tunnel 4000
      interface name: l2tpeth0
      offset 0, peer offset 0
    ok
    test_setup_l2tp (__main__.IPL2tpTests) ... Tunnel 3000, encap UDP
      From 192.168.11.12 to 192.168.11.13
      Peer tunnel 4000
      UDP source / dest ports: 5000/6000
      UDP checksum: disabled
    Session 1000 in tunnel 3000
      Peer session 2000, tunnel 4000
      interface name: l2tpeth0
      offset 0, peer offset 0
    Tunnel 4000, encap UDP
      From 192.168.11.13 to 192.168.11.12
      Peer tunnel 3000
      UDP source / dest ports: 6000/5000
      UDP checksum: disabled
    Tunnel 3000, encap UDP
      From 192.168.11.12 to 192.168.11.13
      Peer tunnel 4000
      UDP source / dest ports: 5000/6000
      UDP checksum: disabled
    Session 2000 in tunnel 4000
      Peer session 1000, tunnel 3000
      interface name: l2tpeth1
      offset 0, peer offset 0
    1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
        link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    2: enp0s31f6: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN mode DEFAULT group default qlen 1000
        link/ether 8c:16:45:6c:83:b9 brd ff:ff:ff:ff:ff:ff
    3: wlp4s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DORMANT group default qlen 1000
        link/ether 7c:76:35:ea:89:90 brd ff:ff:ff:ff:ff:ff
    4: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1360 qdisc fq_codel state UNKNOWN mode DEFAULT group default qlen 100
        link/none
    92: gre0@NONE: <NOARP> mtu 1476 qdisc noop state DOWN mode DEFAULT group default qlen 1000
        link/gre 0.0.0.0 brd 0.0.0.0
    93: gretap0@NONE: <BROADCAST,MULTICAST> mtu 1462 qdisc noop state DOWN mode DEFAULT group default qlen 1000
        link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
    94: erspan0@NONE: <BROADCAST,MULTICAST> mtu 1446 qdisc noop state DOWN mode DEFAULT group default qlen 1000
        link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
    100: ip6tnl0@NONE: <NOARP> mtu 1452 qdisc noop state DOWN mode DEFAULT group default qlen 1000
        link/tunnel6 :: brd ::
    101: ip6gre0@NONE: <NOARP> mtu 1448 qdisc noop state DOWN mode DEFAULT group default qlen 1000
        link/gre6 :: brd ::
    104: tunl0@NONE: <NOARP> mtu 1480 qdisc noop state DOWN mode DEFAULT group default qlen 1000
        link/ipip 0.0.0.0 brd 0.0.0.0
    117: sit0@NONE: <NOARP> mtu 1480 qdisc noop state DOWN mode DEFAULT group default qlen 1000
        link/sit 0.0.0.0 brd 0.0.0.0
    126: ip_vti0@NONE: <NOARP> mtu 1480 qdisc noop state DOWN mode DEFAULT group default qlen 1000
        link/ipip 0.0.0.0 brd 0.0.0.0
    168: test-peer@veth-test: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
        link/ether 96:03:08:d2:65:40 brd ff:ff:ff:ff:ff:ff
    169: veth-test@test-peer: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
        link/ether c2:8c:3b:9f:ea:32 brd ff:ff:ff:ff:ff:ff
    170: l2tpeth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1488 qdisc fq_codel state UNKNOWN mode DEFAULT group default qlen 1000
        link/ether 76:41:ec:b9:d2:75 brd ff:ff:ff:ff:ff:ff
    171: l2tpeth1: <BROADCAST,MULTICAST> mtu 65481 qdisc noop state DOWN mode DEFAULT group default qlen 1000
        link/ether 8e:7f:ab:21:a2:ea brd ff:ff:ff:ff:ff:ff
    PING 10.42.1.2 (10.42.1.2) 56(84) bytes of data.
    64 bytes from 10.42.1.2: icmp_seq=1 ttl=64 time=0.013 ms
    64 bytes from 10.42.1.2: icmp_seq=2 ttl=64 time=0.043 ms
    64 bytes from 10.42.1.2: icmp_seq=3 ttl=64 time=0.066 ms
    64 bytes from 10.42.1.2: icmp_seq=4 ttl=64 time=0.045 ms
    64 bytes from 10.42.1.2: icmp_seq=5 ttl=64 time=0.041 ms
    --- 10.42.1.2 ping statistics ---
    5 packets transmitted, 5 received, 0% packet loss, time 4126ms
    rtt min/avg/max/mdev = 0.013/0.041/0.066/0.018 ms
    ok
    
    ----------------------------------------------------------------------
    Ran 3 tests in 4.322s
    
    OK
    :: [ 15:21:21 ] :: [   PASS   ] :: Command '/usr/bin/python3 /usr/bin/ip-l2tp-tests.py' (Expected 0, got 0)
    :: [ 15:21:21 ] :: [   PASS   ] :: Command '/usr/bin/python3 /usr/bin/ip-l2tp-tests.py' (Expected 0, got 0)
    ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
    ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
    ::   Duration: 5s
    ::   Duration: 5s
    ::   Assertions: 1 good, 0 bad
    ::   Assertions: 1 good, 0 bad
    ::   RESULT: PASS
    ::   RESULT: PASS
    
    ```