bridge: bad error handling when adding invalid ether address

This fixes an crash when empty bond device is added to a bridge.
If an interface with invalid ethernet address (all zero) is added
to a bridge, then bridge code detects it when setting up the forward
databas entry. But the error unwind is broken, the bridge port object 
can get freed twice: once when ref count went to zeo, and once by kfree.
Since object is never really accessible, just free it.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>