update PacketSender interface

java/src/com/zerotier/sdk/PacketSender.java

@@ -37,11 +37,13 @@ public interface PacketSender {
      * on failure. Note that success does not (of course) guarantee packet
      * delivery. It only means that the packet appears to have been sent.</p>
      *
-     * @param addr {@link InetSocketAddress} to send to
+     * @param localAddr {@link InetSocketAddress} to send from.  Set to null if not specified.
+     * @param remoteAddr {@link InetSocketAddress} to send to
      * @param packetData data to send
      * @return 0 on success, any error code on failure.
      */
     public int onSendPacketRequested(
-            InetSocketAddress addr,
+            InetSocketAddress localAddr,
+            InetSocketAddress remoteAddr,
             byte[] packetData);
 }