net/mlx5e: Avoid creating tunnel headers for local route

It could be local and remote are on the same machine and the route
result will be a local route which will result in creating encap id
with src/dst mac address of 0.

Fixes: a54e20b4 ("net/mlx5e: Add basic TC tunnel set action for SRIOV offloads")
Signed-off-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>