Add EthernetClient getSocketNumber() function

libraries/Ethernet/src/EthernetClient.cpp

@@ -171,3 +171,7 @@ EthernetClient::operator bool() {
 bool EthernetClient::operator==(const EthernetClient& rhs) {
   return _sock == rhs._sock && _sock != MAX_SOCK_NUM && rhs._sock != MAX_SOCK_NUM;
 }
+
++uint8_t EthernetClient::getSocketNumber () {
++	return _sock;
++}

libraries/Ethernet/src/EthernetClient.h

@@ -28,6 +28,7 @@ public:
   virtual bool operator!=(const bool value) { return bool() != value; }
   virtual bool operator==(const EthernetClient&);
   virtual bool operator!=(const EthernetClient& rhs) { return !this->operator==(rhs); };
+  uint8_t getSocketNumber();
 
   friend class EthernetServer;