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: Yi Zhao <yi.zhao@windriver.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 0889209..671a1d0 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -2450,7 +2450,7 @@
 
 #ifdef CONFIG_COMPAT
 	if (in_compat_syscall())
-		return -ENOTSUPP;
+		return -EOPNOTSUPP;
 #endif
 
 	type = nlh->nlmsg_type;