vxlan: make vxlan_sock_add and vxlan_sock_release complementary

vxlan: make vxlan_sock_add and vxlan_sock_release complementary

Make vxlan_sock_add both alloc the socket and attach it to vxlan_dev. Let
vxlan_sock_release accept vxlan_dev as its parameter instead of vxlan_sock.

This makes vxlan_sock_add and vxlan_sock release complementary. It reduces
code duplication in the next patch.

Orabug: 29755932

Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 205f356d165033443793a97a668a203a79a8723a)

Reviewed-by: Rama Nichanamatlu <rama.nichanamatlu@oracle.com>
Signed-off-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>