[ONOS-5060] Bug fix for pNAT handler in OpenstackRouting

Sets the dst mac address of the packet as DEFAULT_EXTERNAL_ROUTER_MAC when sending out the packet using packetService.

Change-Id: I79d72539db1bb6cd3e88c4349d0f23dbfe4c57b7
diff --git a/apps/openstacknetworking/routing/src/main/java/org/onosproject/openstacknetworking/routing/OpenstackPnatHandler.java b/apps/openstacknetworking/routing/src/main/java/org/onosproject/openstacknetworking/routing/OpenstackPnatHandler.java
index 3b40aee..b6c998a 100644
--- a/apps/openstacknetworking/routing/src/main/java/org/onosproject/openstacknetworking/routing/OpenstackPnatHandler.java
+++ b/apps/openstacknetworking/routing/src/main/java/org/onosproject/openstacknetworking/routing/OpenstackPnatHandler.java
@@ -190,6 +190,7 @@
         iPacket.setSourceAddress(externalIp.toString());
         iPacket.resetChecksum();
         iPacket.setParent(ethernet);
+        ethernet.setDestinationMACAddress(DEFAULT_EXTERNAL_ROUTER_MAC);
         ethernet.setPayload(iPacket);
 
         treatment.setOutput(gatewayService.getUplinkPort(deviceId));