[IPV6]: Do not change protocol for raw IPv6 sockets.

It is not allowed to change underlying protocol for
   int fd = socket(PF_INET6, SOCK_RAW, IPPROTO_UDP);

Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>