ipv6: Fix the return value of Set Hop-by-Hop options header with NULL data pointer

When Set Hop-by-Hop options header with NULL data
pointer and optlen is not zero use setsockopt(),
the kernel successfully return 0 instead of
return error EINVAL or EFAULT.

This patch fix the problem.

Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>