lnst.spec: fix selinux label of lnst-slave
    
    This patch relabels the lnst-slave executable to the unconfined_exec_t
    type. This fixes our issues with lnst-slave, started by systemd, not
    being able to properly use tcpdump and other netutils.
    
    Signed-off-by: Ondrej Lichtner <olichtne@redhat.com>
    Signed-off-by: Jiri Pirko <jiri@resnulli.us>