vxlan: support both IPv4 and IPv6 sockets in a single vxlan device

vxlan: support both IPv4 and IPv6 sockets in a single vxlan device

For metadata based vxlan interface, open both IPv4 and IPv6 socket. This is
much more user friendly: it's not necessary to create two vxlan interfaces
and pay attention to using the right one in routing rules.

Orabug: 29755932

Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit b1be00a6c39fda2ec380e168d7bcf96fb8c9da42)

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>
Conflicts:
	drivers/net/vxlan.c

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