Fix flush() behaviour on a bunch of classes/libraries

hardware/arduino/avr/libraries/SoftwareSerial/SoftwareSerial.cpp

@@ -469,13 +469,7 @@ size_t SoftwareSerial::write(uint8_t b)
 
 void SoftwareSerial::flush()
 {
-  if (!isListening())
-    return;
-
-  uint8_t oldSREG = SREG;
-  cli();
-  _receive_buffer_head = _receive_buffer_tail = 0;
-  SREG = oldSREG;
+  // There is no tx buffering, simply return
 }
 
 int SoftwareSerial::peek()

libraries/Ethernet/src/EthernetUdp.cpp

@@ -118,7 +118,12 @@ size_t EthernetUDP::write(const uint8_t *buffer, size_t size)
 int EthernetUDP::parsePacket()
 {
   // discard any remaining bytes in the last packet
-  flush();
+  while (_remaining) {
+    // could this fail (loop endlessly) if _remaining > 0 and recv in read fails?
+    // should only occur if recv fails after telling us the data is there, lets
+    // hope the w5100 always behaves :)
+    read();
+  }
 
   if (recvAvailable(_sock) > 0)
   {
@@ -206,14 +211,7 @@ int EthernetUDP::peek()
 
 void EthernetUDP::flush()
 {
-  // could this fail (loop endlessly) if _remaining > 0 and recv in read fails?
-  // should only occur if recv fails after telling us the data is there, lets
-  // hope the w5100 always behaves :)
-
-  while (_remaining)
-  {
-    read();
-  }
+  // TODO: we should wait for TX buffer to be emptied
 }
 
 /* Start EthernetUDP socket, listening at local port PORT */

libraries/WiFi/src/WiFiClient.cpp

@@ -140,8 +140,7 @@ int WiFiClient::peek() {
 }
 
 void WiFiClient::flush() {
-  while (available())
-    read();
+  // TODO: a real check to ensure transmission has been completed
 }
 
 void WiFiClient::stop() {

libraries/WiFi/src/WiFiUdp.cpp

@@ -155,8 +155,7 @@ int WiFiUDP::peek()
 
 void WiFiUDP::flush()
 {
-  while (available())
-    read();
+  // TODO: a real check to ensure transmission has been completed
 }
 
 IPAddress  WiFiUDP::remoteIP()