netfilter: nftables: Add __printf() attribute

nft_request_module calls vsnprintf() using parameters passed to it.
Make the function with __printf() attribute so the compiler can check
the format and arguments.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -581,7 +581,8 @@ struct nft_module_request {
 };
 
 #ifdef CONFIG_MODULES
-static int nft_request_module(struct net *net, const char *fmt, ...)
+static __printf(2, 3) int nft_request_module(struct net *net, const char *fmt,
+					     ...)
 {
 	char module_name[MODULE_NAME_LEN];
 	struct nft_module_request *req;