udptunnels: Call handle_offloads after inserting vlan tag.

[ Upstream commit b736a623bd099cdf5521ca9bd03559f3bc7fa31c ]

handle_offloads() calls skb_reset_inner_headers() to store
the layer pointers to the encapsulated packet. However, we
currently push the vlag tag (if there is one) onto the packet
afterwards. This changes the MAC header for the encapsulated
packet but it is not reflected in skb->inner_mac_header, which
breaks GSO and drivers which attempt to use this for encapsulation
offloads.

Fixes: 1eaa8178 ("vxlan: Add tx-vlan offload support.")
Signed-off-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>