mlxsw: spectrum_router: Use nexthop group type in hash table key

Both IPv4 and IPv6 nexthop groups are hashed in the same table. The
protocol field is used to indicate how the hash should be computed for
each group.

When nexthop group objects are supported, the hash will be computed for
them based on the nexthop identifier.

To differentiate between all the nexthop group types, encode the type of
the group in the key instead of the protocol.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>