rocker: Register FIB notifier before creating ports

We can miss FIB notifications sent between the time the ports were
created and the FIB notification block registered.

Instead of receiving these notifications only when they are replayed for
the FIB notification block during registration, just register the
notification block before the ports are created.

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