swss: gearsyncd should return 0 on exit (sonic-net#1376)

- changes made to supervisord conf require gearsyncd to return 0 otherwise
restarts are performed, fail, and swss docker exits
- originally, gearsyncd did not exit, and if it did, 1 exit code was returned
to indicate failure. We converted this to do its job and exit, but did not
correct the exit code.
- prior state was not a problem until changes that are yet to merge for
sonic-buildimage supervisord conf made returning a 1 problematic.

  Signed-off-by: syd.logan@broadcom.com

gearsyncd/gearsyncd.cpp

@@ -67,7 +67,7 @@ int main(int argc, char **argv)
             break;
         case 'h':
             usage();
-            return 1;
+            return EXIT_FAILURE;
         default: /* '?' */
             usage();
             return EXIT_FAILURE;
@@ -105,7 +105,7 @@ int main(int argc, char **argv)
         cerr << "Exception \"" << e.what() << "\" had been thrown in gearsyncd daemon" << endl;
         return EXIT_FAILURE;
     }
-    return 1;
+    return EXIT_SUCCESS;
 }
 
 bool handleGearboxConfigFromConfigDB(ProducerStateTable &p, DBConnector &cfgDb, bool warm)