bridge: Simplify interface for ATM LANE

This patch changes FDB entry check for ATM LANE bridge integration.
There's no point in holding a FDB entry around SKB building.

br_fdb_get()/br_fdb_put() pair are changed into single br_fdb_test_addr()
hook that checks if the addr has FDB entry pointing to other port
to the one the request arrived on.

FDB entry refcounting is removed as it's not used anywhere else.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>