vxlan: simplify metadata_dst usage in vxlan_rcv

Now when the packet is scrubbed early, the metadata_dst can be assigned to
the skb as soon as it is allocated. This simplifies the error cleanup path,
as the dst will be freed by kfree_skb. It is also not necessary to pass it
as a parameter to functions anymore.

Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>