bridge: Check if vlan filtering is enabled only once.

The bridge code checks if vlan filtering is enabled on both
ingress and egress.   When the state flip happens, it
is possible for the bridge to currently be forwarding packets
and forwarding behavior becomes non-deterministic.  Bridge
may drop packets on some interfaces, but not others.

This patch solves this by caching the filtered state of the
packet into skb_cb on ingress.  The skb_cb is guaranteed to
not be over-written between the time packet entres bridge
forwarding path and the time it leaves it.  On egress, we
can then check the cached state to see if we need to
apply filtering information.

Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>