Move one "#ifdef NVLAN" chunk needed only if you're running bridge(4) on

Move one "#ifdef NVLAN" chunk needed only if you're running bridge(4) on
to of vlan(4) from ether_input() to bridge_input().

One of the goal of the if_input() plumbing is to stop doing all possible
pseudo-drivers checks on every packets.  There's no reason that even if
you're not running a bridge(4) you've to run this code.

This change also will also makes it easier to convert vlan(4) to if_input().

Reviewed by Rafael Zalamena and mikeb@, ok markus@