mlxsw: spectrum_mr: Add ipv6 specific operations

Populate the various operation structures meant for IPv6 with logic
unique to that protocol suite.

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>