mlxsw: reg: Give mlxsw_reg_ratr_pack a type parameter

To support IPIP, the driver needs to be able to construct an IPIP
adjacency. Change mlxsw_reg_ratr_pack to take an adjacency type as an
argument. Adjust the one existing caller.

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