module-setup: Choose the first matched gateway in kdump_static_ip
    
    The system may have multiple default route entry. Following is an
    example to show the details.
    
     # ip -6 route list dev eth0
    2620:52:0:1040::/64  proto kernel  metric 256  expires 2591978sec fe80::/64  proto kernel  metric 256
    default via fe80:52:0:1040::1  proto ra  metric 1024  expires 1778sec hoplimit 64
    default via fe80:52:0:1040::2  proto ra  metric 1024  expires 1778sec hoplimit 64
    
    Choose the first matched entry.
    
    Signed-off-by: Minfei Huang <mhuang@redhat.com>
    Acked-by: Baoquan He <bhe@redhat.com>