Support group mods and group stats requests.

Added support for match IPv4 destination address.

Change-Id: I8693299f29ba3c45f61b936877d443218e5410c4
diff --git a/internal/pkg/openflow/connection.go b/internal/pkg/openflow/connection.go
index 691644c..af388b2 100644
--- a/internal/pkg/openflow/connection.go
+++ b/internal/pkg/openflow/connection.go
@@ -407,7 +407,7 @@
 			ofc.sendRoleSlaveError(header)
 			return
 		}
-		// TODO handle group mods
+		ofc.handleGroupMod(header.(ofp.IGroupMod))
 	}
 }