net/mlx5: Add case for FS_FT_NIC_TX FT in MLX5_CAP_FLOWTABLE_TYPE

Commit 16f1c5bb

 ("net/mlx5: Check device capability for maximum flow
counters") added MLX5_CAP_FLOWTABLE_TYPE but forgot to account
for FS_FT_NIC_TX case in the expression.

Although the expression will return 1 for this case instead of the
actual cap, there isn't currently no known side affects of
missing this case.

Add the FS_FT_NIC_TX case.

Signed-off-by: Paul Blakey <paulb@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>