mlxsw: spectrum_router: Configure RIFs based on IPv6 addresses

When a netdev is configured with an IP address a router interface (RIF)
should be configured for it in the device. Allow configuration of RIFs
based on IPv6 address notifications as well as IPv4.

Note that the RIF exists as long as an IP address is configured on the
netdev, regardless of the address family.

Signed-off-by: Arkadi Sharshevsky <arkadis@mellanox.com>
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>