mlxsw: spectrum_router: Pass array of routes to route handling functions

Prepare the driver to handle multiple routes in a single notification by
passing an array of routes to the functions that actually add / delete a
route.

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