vxlan: simplify exception handling

vxlan egress path error handling has became complicated, it
need to handle IPv4 and IPv6 tunnel cases.
Earlier patch removes vlan handling from vxlan_build_skb(), so
vxlan_build_skb does not need to free skb and we can simplify
the xmit path by having single error handling for both type of
tunnels.

Signed-off-by: Pravin B Shelar <pshelar@ovn.org>
Acked-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>