inet: shrink struct flowi_common

I am looking at syzbot reports triggering kernel stack overflows
involving a cascade of ipvlan devices.

We can save 8 bytes in struct flowi_common.

This patch alone will not fix the issue, but is a start.

Fixes: 24ba1440 ("route: Add multipath_hash in flowi_common to make user-define hash")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: wenxu <wenxu@ucloud.cn>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20231025141037.3448203-1-edumazet@google.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

include/net/flow.h

@@ -40,8 +40,8 @@ struct flowi_common {
 #define FLOWI_FLAG_KNOWN_NH		0x02
 	__u32	flowic_secid;
 	kuid_t  flowic_uid;
-	struct flowi_tunnel flowic_tun_key;
 	__u32		flowic_multipath_hash;
+	struct flowi_tunnel flowic_tun_key;
 };
 
 union flowi_uli {