Revert "bridge: Let bridge not age 'externally' learnt FDB entries, they are...

Revert "bridge: Let bridge not age 'externally' learnt FDB entries, they are removed when 'external' entity notifies the aging"

This reverts commit 9a05dde5.

Requested by Scott Feldman.

Signed-off-by: David S. Miller <davem@davemloft.net>