net: vlan: Allow VLAN count to be set to 0

If VLAN count is set to 0, then only priority tagged VLAN frames
that have tag value 0 can be received. Also this means that VLAN
interfaces are not created which can save memory if you do not need
to receive any other VLAN frames than those tagged with value 0.

Fixes #84023

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>