This commit makes scattered TX support entirely optional by moving it to a separate function that is only available when MLX4_PMD_SGE_WR_N > 1. Improves performance when scattered support is not needed. Signed-off-by: Alex Rosenbaum <alexr@mellanox.com> Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>