sfc: parse mangle actions (NAT) in conntrack entries

The MAE can edit either address, L4 port, or both, for either source
 or destination.  These can't be mixed; i.e. it can edit source addr
 and source port, but not (say) source addr and dest port.

Reviewed-by: Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@amd.com>
Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>