net/mlx5: fix flow modify action validation

net/mlx5: fix flow modify action validation

The introduced MODIFY_FIELD action was used to manipulate
the packet header field through copy or set operations.

These modify header actions should be counted as one action
in low level, the current code used wrong actions flags
checking for modify field action.

This patch update the action flags checking into the correct
MODIFY_HDR_ACTIONS set.

Fixes: 641dbe4fb053 ("net/mlx5: support modify field flow action")
Cc: stable@dpdk.org
Signed-off-by: Jiawei Wang <jiaweiw@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>