libsysutils: Fix some bugs in NetlinkListener and NetlinkEvent

Signed-off-by: San Mehat <san@android.com>
diff --git a/include/sysutils/NetlinkListener.h b/include/sysutils/NetlinkListener.h
index 6dcc005..2880046 100644
--- a/include/sysutils/NetlinkListener.h
+++ b/include/sysutils/NetlinkListener.h
@@ -26,7 +26,9 @@
 public:
     NetlinkListener(int socket);
     virtual ~NetlinkListener() {}
+
 protected:
     virtual bool onDataAvailable(SocketClient *cli);
+    virtual void onEvent(NetlinkEvent *evt) = 0;
 };
 #endif