net/mlx5: fix internal root table flow priority

net/mlx5: fix internal root table flow priority

When creating internal transfer flow on root table with lowest
priority, the flow was created with max UINT32_MAX priority. It is wrong
since the flow is created in kernel and  max priority supported is 16.

This patch fixes this by adding internal flow check.

Fixes: 5f8ae44dd454 ("net/mlx5: enlarge maximal flow priority")
Cc: stable@dpdk.org
Signed-off-by: Xueming Li <xuemingl@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>