bridge: Call vlan_vid_del for all vids at nbp_vlan_flush

We should call vlan_vid_del for all vids at nbp_vlan_flush to prevent
vid_info->refcount from being leaked when detaching a bridge port.

Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>