mlxsw: spectrum_acl: Convert flower-based mirroring to new SPAN API

In flower-based mirroring, mirroring is done with ACLs and the SPAN
agent is not bound to a port. Instead its identifier is specified in an
ACL action.

Convert this type of mirroring to use the new API.

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