vxlan: avoid using stale vxlan socket.

vxlan: avoid using stale vxlan socket.

When vxlan device is closed vxlan socket is freed. This
operation can race with vxlan-xmit function which
dereferences vxlan socket. Following patch uses RCU
mechanism to avoid this situation.

Orabug: 29927196

Reviewed-by: Rama Nichanamatlu <rama.nichanamatlu@oracle.com>
Signed-off-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit c6fcc4fc5f8b592600c7409e769ab68da0fb1eca)
Signed-off-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	drivers/net/vxlan.c

Signed-off-by: Brian Maly <brian.maly@oracle.com>