Add initial dump() method to NetdNativeService

This is called by "dumpsys netd".

Bug: 27239233
Change-Id: I27fb308f8067243ff241a6f8fd6a83f406087d2a
diff --git a/server/Network.h b/server/Network.h
index 3af53d9..8949dd1 100644
--- a/server/Network.h
+++ b/server/Network.h
@@ -48,6 +48,8 @@
     virtual int removeInterface(const std::string& interface) WARN_UNUSED_RESULT = 0;
     int clearInterfaces() WARN_UNUSED_RESULT;
 
+    std::string toString() const;
+
 protected:
     explicit Network(unsigned netId);