check transportchannelprovider endpoint not the default endpoint.

Author: rmehta19

gax-java/gax/src/main/java/com/google/api/gax/rpc/EndpointContext.java

@@ -327,7 +327,9 @@ boolean shouldUseS2A() {
       }
 
       // If a custom endpoint is being used, skip S2A.
-      if (!Strings.isNullOrEmpty(clientSettingsEndpoint())) {
+      if (!Strings.isNullOrEmpty(clientSettingsEndpoint())
+          || (transportChannelProviderEndpoint()
+              == buildEndpointTemplate(serviceName(), resolvedUniverseDomain()))) {
         return false;
       }