ipv6 netns: init net is used to set bindv6only for new sock

The bindv6only is tuned via sysctl. It is already on a struct net
and per-net sysctls allow for its modification (ipv6_sysctl_net_init).

Despite this the value configured in the init net is used for the
rest of them.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>