fix(ip): netns list parsing with netnsids included

ip netns output may include netnsid if set since
https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/commit/?id=d182ee1307c7a83b581d8f6d473bbce2004420c0

Author: remijouannet

completions/ip

@@ -360,7 +360,9 @@ _ip()
                 delete | exec | pids | set)
                     [[ $prev == "$subcmd" ]] &&
                         COMPREPLY=($(compgen -W "$(
-                            $1 -c=never netns list 2>/dev/null || $1 netns list
+                            {
+                                $1 -c=never netns list 2>/dev/null || $1 netns list
+                            } | awk '{print $1}'
                         )" -- "$cur"))
                     ;;
                 *)