mlxsw: spectrum_acl: Introduce new rehash context struct and save hint_priv there

Prepare for continued migration. Introduce a new structure to track
rehash context and save hint_priv into it.

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