mlxsw: spectrum: router: Add support for address validator notifier

Add support for inetaddr_validator and inet6addr_validator. The
notifiers provide a means for validating ipv4 and ipv6 addresses
before the addresses are installed and on failure the error
is propagated back to the user.

Signed-off-by: David Ahern <dsahern@gmail.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>