net/mlx5: DR, Handle FT action in a separate function

As preparation for range action support, moving the handling
of final ICM address for flow table action to a separate function.

Signed-off-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Reviewed-by: Alex Vesker <valex@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>