net/mlx5e: Offload rule only when all encaps are valid

The cited commit adds a for loop to support multiple encapsulations.
But it only checks if the last encap is valid.

Fix it by setting slow path flag when one of the encap is invalid.

Fixes: f493f155 ("net/mlx5e: Move flow attr reformat action bit to per dest flags")
Signed-off-by: Chris Mi <cmi@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>