sfc: introduce pedit add actions on the ipv4 ttl field

Introduce pedit add actions and use it to achieve decrement ttl offload.
Decrement ttl can be achieved by adding 0xff to the ttl field.

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