selftests: mptcp: add struct params in mptcp_diag

This patch adds a struct named 'params' to save 'target_token' and other
future parameters. This structure facilitates future function expansions.

Co-developed-by: Geliang Tang <[e-mail]>
Signed-off-by: Geliang Tang <[e-mail]>
Signed-off-by: Gang Yan <[e-mail]>
Reviewed-by: Matthieu Baerts (NGI0) <[e-mail]>
Signed-off-by: Matthieu Baerts (NGI0) <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

tools/testing/selftests/net/mptcp/mptcp_diag.c

···
 #define IPPROTO_MPTCP 262
 #endif
 
+struct params {
+	__u32 target_token;
+};
+
 struct mptcp_info {
 	__u8	mptcpi_subflows;
 	__u8	mptcpi_add_addr_signal;
···
 	close(fd);
 }
 
-static void parse_opts(int argc, char **argv, __u32 *target_token)
+static void parse_opts(int argc, char **argv, struct params *p)
 {
 	int c;
 
···
 			die_usage(0);
 			break;
 		case 't':
-			sscanf(optarg, "%x", target_token);
+			sscanf(optarg, "%x", &p->target_token);
 			break;
 		default:
 			die_usage(1);
···
 
 int main(int argc, char *argv[])
 {
-	__u32 target_token;
+	struct params p = { 0 };
 
-	parse_opts(argc, argv, &target_token);
-	get_mptcpinfo(target_token);
+	parse_opts(argc, argv, &p);
+
+	if (p.target_token)
+		get_mptcpinfo(p.target_token);
 
 	return 0;
 }