ip: fix exit codes

Alternative fix to problem reported by: Bin Li
The issue is came from https://bugzilla.novell.com/show_bug.cgi?id=681952.

In any previous version (since suse ... 10.0?), ip addr add always returned
the error code 2 in case the ip address is already set on the interface:

    inet 172.16.2.3/24 brd 172.16.2.255 scope global bond0
RTNETLINK answers: File exists
2

On 11.4, it returns the exit code 254:

    inet 172.16.1.1/24 brd 172.16.1.255 scope global eth0
RTNETLINK answers: File exists
254

This of course causes ifup to return an error in this quite common case..

ip/ip.c

@@ -91,31 +91,32 @@ static int do_cmd(const char *argv0, int argc, char **argv)
 	const struct cmd *c;
 
 	for (c = cmds; c->cmd; ++c) {
-		if (matches(argv0, c->cmd) == 0)
-			return c->func(argc-1, argv+1);
+		if (matches(argv0, c->cmd) == 0) {
+			return -(c->func(argc-1, argv+1));
+		}
 	}
 
 	fprintf(stderr, "Object \"%s\" is unknown, try \"ip help\".\n", argv0);
-	return -1;
+	return EXIT_FAILURE;
 }
 
 static int batch(const char *name)
 {
 	char *line = NULL;
 	size_t len = 0;
-	int ret = 0;
+	int ret = EXIT_SUCCESS;
 
 	if (name && strcmp(name, "-") != 0) {
 		if (freopen(name, "r", stdin) == NULL) {
 			fprintf(stderr, "Cannot open file \"%s\" for reading: %s\n",
 				name, strerror(errno));
-			return -1;
+			return EXIT_FAILURE;
 		}
 	}
 
 	if (rtnl_open(&rth, 0) < 0) {
 		fprintf(stderr, "Cannot open rtnetlink\n");
-		return -1;
+		return EXIT_FAILURE;
 	}
 
 	cmdlineno = 0;
@@ -129,7 +130,7 @@ static int batch(const char *name)
 
 		if (do_cmd(largv[0], largc, largv)) {
 			fprintf(stderr, "Command failed %s:%d\n", name, cmdlineno);
-			ret = 1;
+			ret = EXIT_FAILURE;
 			if (!force)
 				break;
 		}