inotify: also detect VLAN id from "vlan\d+" ifaces

inotify: also detect VLAN id from "vlan\d+" ifaces

We support also vlanX, with X being a integer for the VLAN id, as
valid vlan iface name, so support that too here.

and make the dev name check for definedness, even if "0" is currently
not really supported (officially) it is still a valid iface name for
the kernel (which takes any byte).

The VLAN id is in the range of [2, 4094] (inclusive) so defined check
is not required there.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>