datapath: backport: vxlan: correctly handle ipv6.disable module parameter

datapath: backport: vxlan: correctly handle ipv6.disable module parameter

upstream commit:
    commit d074bf9600443403aa24fbc12c1f18eadc90f5aa
    Author: Jiri Benc <jbenc@redhat.com>
    Date:   Thu Apr 27 21:24:35 2017 +0200

    vxlan: correctly handle ipv6.disable module parameter

    When IPv6 is compiled but disabled at runtime, __vxlan_sock_add returns
    -EAFNOSUPPORT. For metadata based tunnels, this causes failure of the whole
    operation of bringing up the tunnel.

    Ignore failure of IPv6 socket creation for metadata based tunnels caused by
    IPv6 not being available.

    Fixes: b1be00a6c39f ("vxlan: support both IPv4 and IPv6 sockets in a single vxlan device")
    Signed-off-by: Jiri Benc <jbenc@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Pravin B Shelar <pshelar@ovn.org>
Acked-by: Joe Stringer <joe@ovn.org>