Rework setHostname for WiFi STA

Fixes: https://github.com/espressif/arduino-esp32/issues/2537

libraries/WiFi/src/WiFiGeneric.cpp

@@ -379,6 +379,7 @@ esp_err_t WiFiGenericClass::_eventCallback(void *arg, system_event_t *event, wif
     } else if(event->event_id == SYSTEM_EVENT_STA_START) {
         WiFiSTAClass::_setStatus(WL_DISCONNECTED);
         setStatusBits(STA_STARTED_BIT);
+        tcpip_adapter_set_hostname(TCPIP_ADAPTER_IF_STA, WiFiSTAClass::_hostname.c_str());
     } else if(event->event_id == SYSTEM_EVENT_STA_STOP) {
         WiFiSTAClass::_setStatus(WL_NO_SHIELD);
         clearStatusBits(STA_STARTED_BIT | STA_CONNECTED_BIT | STA_HAS_IP_BIT | STA_HAS_IP6_BIT);

libraries/WiFi/src/WiFiSTA.cpp

@@ -71,6 +71,7 @@ static bool sta_config_equal(const wifi_config_t& lhs, const wifi_config_t& rhs)
 
 bool WiFiSTAClass::_autoReconnect = true;
 bool WiFiSTAClass::_useStaticIp = false;
+String WiFiSTAClass::_hostname = "esp32-arduino";
 
 static wl_status_t _sta_status = WL_NO_SHIELD;
 static EventGroupHandle_t _sta_status_group = NULL;
@@ -283,7 +284,6 @@ bool WiFiSTAClass::config(IPAddress local_ip, IPAddress gateway, IPAddress subne
     }
 
     tcpip_adapter_ip_info_t info;
-    log_d("STA IP uint32_t: %u.%u.%u.%u\n", local_ip[0], local_ip[1], local_ip[2], local_ip[3]);
 
     if(local_ip != (uint32_t)0x00000000 && local_ip != INADDR_NONE){
         info.ip.addr = static_cast<uint32_t>(local_ip);
@@ -637,6 +637,7 @@ const char * WiFiSTAClass::getHostname()
  */
 bool WiFiSTAClass::setHostname(const char * hostname)
 {
+    _hostname = hostname;
     if(WiFiGenericClass::getMode() == WIFI_MODE_NULL){
         return false;
     }

libraries/WiFi/src/WiFiSTA.h

@@ -86,6 +86,7 @@ public:
     int8_t RSSI();
 
     static void _setStatus(wl_status_t status);
+    static String _hostname;
 protected:
     static bool _useStaticIp;
     static bool _autoReconnect;