mlxsw: spectrum_router: Replay IP NETDEV_UP on device enslavement

Enslaving of front panel ports (and their uppers) to netdevices that
already have uppers is currently forbidden. When this is permitted, any
uppers with IP addresses need to have the NETDEV_UP inetaddr event
replayed, so that any RIFs are created.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Danielle Ratson <danieller@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>