mlxsw: spectrum_router: Prepare function for router lock introduction

The function removes the FDB entry that directs the macvlan's MAC to the
router port. It is called from both the netdev notifier block and the
inetaddr notifier block that will soon hold the router lock.

Make sure that only the netdev notifier calls the exported version, so
that is will take the router lock, which will already be held by the
inetaddr notifier.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>