net/mlx5: fix drop action in tunnel offload mode

net/mlx5: fix drop action in tunnel offload mode

Tunnel offload mode allows application to restore partially offloaded
tunneled packets to its original state.
The mode was designed to optimize packet recovery. It must not
block flow actions that are allowed by MLX5 PMD.

The patch allows tunnel offload match rules to use drop flow action.

Fixes: 4ec6360de37d ("net/mlx5: implement tunnel offload")
Cc: stable@dpdk.org
Signed-off-by: Gregory Etelson <getelson@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>