rest: do not exit() if execlp() fails

execlp() should not ever fail, but if it ever happens, return -1 instead of
exitting this daemon.

src/rest.c

@@ -1247,7 +1247,7 @@ static int og_set_client_mode(struct og_dbi *dbi, const char *mac,
 		       "/opt/opengnsys/bin/setclientmode", filename, NULL);
 		syslog(LOG_ERR, "failed script execution (%s:%d)\n",
 		       __func__, __LINE__);
-		exit(EXIT_FAILURE);
+		return -1;
 	} else {
 		wait(&status);
 	}