interface: handle name@link from iproute2

Since #1090, iproute2 is preferred over ifconfig, however iproute2
provide the list of network interface in name@link in case an interface
is bound to another one (such as macvtap for example), while the real
interface name is not.

  $ ip link show
  2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
      link/ether 48:21:0b:52:19:22 brd ff:ff:ff:ff:ff:ff
  4: eth0.128@eth0: <BROADCAST,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
      link/ether 48:21:0b:52:19:22 brd ff:ff:ff:ff:ff:ff

bash-completion using name@link as provided by iproute2 output then
provide such name in auto completion list, leading to invalid interface
name when auto completing tcpdump arguments.

  $ tcpdump -i <TAB>
  eth0      eth0.128@eth0

This commit handle this use case to drop link name after name@.

  $ tcpdump -i <TAB>
  eth0      eth0.128

See: #1090
See: https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/tree/lib/utils.c?h=v6.15.0#n1306

Author: bjacquin

bash_completion

@@ -1821,7 +1821,7 @@ _comp_compgen_available_interfaces()
             ip -c=never link show || ip link show || ifconfig -a
         fi
     } 2>/dev/null | _comp_awk \
-        '/^[^ \t]/ { if ($1 ~ /^[0-9]+:/) { print $2 } else { print $1 } }')" &&
+        '/^[^ \t]/ { if ($1 ~ /^[0-9]+:/) { sub(/@.*/, "", $2); print $2 } else { print $1 } }')" &&
         _comp_compgen -U generated set "${generated[@]%:}"
 }