net: tipc: Add __printf() markup to fix -Wsuggest-attribute=format

net/tipc/netlink_compat.c: In function ‘tipc_tlv_sprintf’:
net/tipc/netlink_compat.c:137:2: warning: function ‘tipc_tlv_sprintf’ might be a candidate for ‘gnu_printf’ format attribute [-Wsuggest-attribute=format]
  137 |  n = vscnprintf(buf, rem, fmt, args);
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/tipc/netlink_compat.c

@@ -118,7 +118,8 @@ static void tipc_tlv_init(struct sk_buff *skb, u16 type)
 	skb_put(skb, sizeof(struct tlv_desc));
 }
 
-static int tipc_tlv_sprintf(struct sk_buff *skb, const char *fmt, ...)
+static __printf(2, 3) int tipc_tlv_sprintf(struct sk_buff *skb,
+					   const char *fmt, ...)
 {
 	int n;
 	u16 len;