ip6_tunnel: set rtnl_link_ops before calling register_netdevice

When creating an ip6tnl tunnel with ip tunnel, rtnl_link_ops is not set
before ip6_tnl_create2 is called. When register_netdevice is called, there
is no linkinfo attribute in the NEWLINK message because of that.

Setting rtnl_link_ops before calling register_netdevice fixes that.

Fixes: 0b112457 ("ip6tnl: add support of link creation via rtnl")
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@redhat.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>