doc: update features supported by mlx

doc: update features supported by mlx

Flow control was not documented as a supported feature
since the first fill of features matrix for mlx drivers.

Flow API and CRC offload flag support in mlx4 were missing in the
feature matrix when they were implemented (see below commits).

Fixes: 46d5736a7049 ("net/mlx4: support basic flow items and actions")
Fixes: ce07b1514d59 ("net/mlx4: fix CRC stripping capability report")
Fixes: e86b85ca757b ("doc: fill nics features matrix for mlx")
Cc: stable@dpdk.org
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Matan Azrad <matan@mellanox.com>