net/mlx5e: Refactor FTE setup code to be more clear

The policy offload logic needs to set flow steering rule that match
on saddr and daddr too, so factor out this code to separate functions,
together with code alignment to netdev coding pattern of relying on
family type.

As part of this change, let's separate more logic from setup_fte_common
to make sure that the function names describe that is done in the
function better than general *common* name.

Reviewed-by: Raed Salem <raeds@nvidia.com>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>