net-next: treewide use is_vlan_dev() helper function.

This patch makes use of is_vlan_dev() function instead of flag
comparison which is exactly done by is_vlan_dev() helper function.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Daniel Jurgens <danielj@mellanox.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Jon Maxwell <jmaxwell37@gmail.com>
Acked-by: Johannes Thumshirn <jth@kernel.org>
Acked-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>