xfrm_user: fix return value from xfrm_user_rcv_msg

It doesn't support to run 32bit 'ip' to set xfrm objdect on 64bit host.
But the return value is unknown for user program:

ip xfrm policy list
RTNETLINK answers: Unknown error 524

Replace ENOTSUPP with EOPNOTSUPP:

ip xfrm policy list
RTNETLINK answers: Operation not supported
Signed-off-by: NYi Zhao <yi.zhao@windriver.com>
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_user.c

@@ -2450,7 +2450,7 @@ static int xfrm_user_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 
 #ifdef CONFIG_COMPAT
 	if (in_compat_syscall())
-		return -ENOTSUPP;
+		return -EOPNOTSUPP;
 #endif
 
 	type = nlh->nlmsg_type;