Fix some new warndings found in build testing.

net/netdev/netdev.h

@@ -468,9 +468,7 @@ int netdev_ipv6_ifconf(FAR struct lifconf *lifc);
  *
  ****************************************************************************/
 
-#ifdef CONFIG_NETDOWN_NOTIFIER
 int netdev_dev_lladdrsize(FAR struct net_driver_s *dev);
-#endif
 
 /****************************************************************************
  * Name: netdown_notifier_setup

net/udp/udp.h

@@ -334,6 +334,27 @@ void udp_ipv6_select(FAR struct net_driver_s *dev);
 
 void udp_poll(FAR struct net_driver_s *dev, FAR struct udp_conn_s *conn);
 
+/****************************************************************************
+ * Name: psock_udp_cansend
+ *
+ * Description:
+ *   psock_udp_cansend() returns a value indicating if a write to the socket
+ *   would block.  It is still possible that the write may block if another
+ *   write occurs first.
+ *
+ * Input Parameters:
+ *   psock    An instance of the internal socket structure.
+ *
+ * Returned Value:
+ *   -ENOSYS (Function not implemented, always have to wait to send).
+ *
+ * Assumptions:
+ *   None
+ *
+ ****************************************************************************/
+
+int psock_udp_cansend(FAR struct socket *psock);
+;
 /****************************************************************************
  * Name: udp_send
  *