[XFRM]: Don't panic in xfrm_user_init

Since xfrm_user can be built as a module it's best not to panic
when something goes wrong in xfrm_user_init.  Call me a wimp for
not fixing netlink_kernel_init's return value :)
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/xfrm/xfrm_user.c

@@ -1237,8 +1237,7 @@ static int __init xfrm_user_init(void)
 
 	xfrm_nl = netlink_kernel_create(NETLINK_XFRM, xfrm_netlink_rcv);
 	if (xfrm_nl == NULL)
-		panic("xfrm_user_init: cannot initialize xfrm_nl\n");
-
+		return -ENOMEM;
 
 	xfrm_register_km(&netlink_mgr);