bridge: Don't put partly initialized fdb into hash

The fdb_create() puts a new fdb into hash with only addr set. This is
not good, since there are callers, that search the hash w/o the lock
and access all the other its fields.

Applies to current netdev tree.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>