Network: Implement ipv6/ipv4 default gateways on EthernetInterface

Currently ipv6/ipv4 default gateway properties on SystemConfiguration
interface which will be deprecated soon.
This commit is to add Default gateway properties implementation on
EthernetInterface.

Test by:
Set ipv4/v6 default gateway properties on ethernet interface.

Signed-off-by: Ravi Teja <raviteja28031990@gmail.com>
Change-Id: I30da81d7ccf9d568a60bfdd179331b4c0d86b149
diff --git a/routing_table.cpp b/routing_table.cpp
index ffbeecb..68a9ee3 100644
--- a/routing_table.cpp
+++ b/routing_table.cpp
@@ -151,16 +151,16 @@
     }
     if (!dstAddr && gateWayAddr)
     {
+        std::string ifNameStr(ifName);
         if (rtMsg->rtm_family == AF_INET)
         {
-            defaultGateway = gatewayStr;
+            defaultGateway[ifNameStr] = gatewayStr;
         }
         else if (rtMsg->rtm_family == AF_INET6)
         {
-            defaultGateway6 = gatewayStr;
+            defaultGateway6[ifNameStr] = gatewayStr;
         }
     }
-
     Entry route(dstStr, gatewayStr, ifName);
     // if there is already existing route for this network
     // then ignore the next one as it would not be used by the