net/mlx5e: Avoid implicit modify hdr for decap drop rule

Currently the driver adds implicit modify hdr action for
decap rules on tunnel devices if the port is an ovs port.
This is also done if the action is drop and makes the modify
hdr redundant and also the FW doesn't support it and will generate
a syndrome.

kernel: mlx5_core 0000:08:00.0: mlx5_cmd_check:777:(pid 102063): SET_FLOW_TABLE_ENTRY(0x936) op_mod(0x0) failed, status bad parameter(0x3), syndrome (0x8708c3)

Fix it by adding the implicit modify hdr only for fwd actions.

Fixes: b16eb3c8 ("net/mlx5: Support internal port as decap route device")
Fixes: 077cdda7

 ("net/mlx5e: TC, Fix memory leak with rules with internal port")
Signed-off-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Ariel Levkovich <lariel@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>