br_allowed_ingress() has two problems.

1. If br_allowed_ingress() is called by br_handle_frame_finish() and
vlan_untag() in br_allowed_ingress() fails, skb will be freed by both
vlan_untag() and br_handle_frame_finish().

2. If br_allowed_ingress() is called by br_dev_xmit() and
br_allowed_ingress() fails, the skb will not be freed.

Fix these two problems by freeing the skb in br_allowed_ingress()
if it fails.
Signed-off-by: NToshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>