vdpa/mlx5: Remove redundant header file inclusion

linux/if_vlan.h is not required.
Remove it.

Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20210823052123.14909-2-elic@nvidia.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>