added method for changing time server

Author: Peeter Normak

NTPClient.cpp

@@ -148,6 +148,10 @@ void NTPClient::setUpdateInterval(unsigned long updateInterval) {
   this->_updateInterval = updateInterval;
 }
 
+void NTPClient::setPoolServerName(const char* poolServerName) {
+    this->_poolServerName = poolServerName;
+}
+
 void NTPClient::sendNTPPacket() {
   // set all bytes in the buffer to 0
   memset(this->_packetBuffer, 0, NTP_PACKET_SIZE);

NTPClient.h

@@ -33,6 +33,13 @@ class NTPClient {
     NTPClient(UDP& udp, const char* poolServerName, long timeOffset);
     NTPClient(UDP& udp, const char* poolServerName, long timeOffset, unsigned long updateInterval);
 
+    /**
+     * Set time server name
+     *
+     * @param poolServerName
+     */
+    void setPoolServerName(const char* poolServerName);
+
     /**
      * Starts the underlying UDP client with the default local port
      */