mlxsw: spectrum_mr: Pass protocol as part of catchall route params

Since commit c011ec1b ("mlxsw: spectrum: Add the multicast routing
offloading logic") spectrum_mr did not populate the protocol portion of
the catcahall_route_params; mr-tcam logic worked correctly for ipv4
since the enum value for MLXSW_SP_L3_PROTO_IPV4 is '0'.

Explicitly fill the protocol as we'll soon need to differentiate between
ipv4 and ipv6.

Signed-off-by: Yuval Mintz <yuvalm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>