vlan: add helper which can be called to see if device is used by vlan

also, remove unused vlan_info definition from header

CC: Patrick McHardy <kaber@trash.net>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>
2 files changed