Revert 8541 wifi client fix (#267)

* Revert "Reimplemented flush in WiFiClient"

---------

Co-authored-by: Me No Dev <me-no-dev@users.noreply.github.com>

Author: Jason2866

.github/ISSUE_TEMPLATE/Issue-report.yml

@@ -41,6 +41,8 @@ body:
       options:
         - latest master (checkout manually)
         - latest development Release Candidate (RC-X)
+        - v2.0.13
+        - v2.0.12
         - v2.0.11
         - v2.0.10
         - v2.0.9

libraries/WiFi/src/WiFiClient.cpp

@@ -158,13 +158,6 @@ class WiFiClientRxBuffer {
     size_t available(){
         return _fill - _pos + r_available();
     }
-
-    void flush(){
-        if(r_available()){
-            fillBuffer();
-        }
-        _pos = _fill;
-    }
 };
 
 class WiFiClientSocketHandle {
@@ -536,7 +529,26 @@ int WiFiClient::available()
 // Though flushing means to send all pending data,
 // seems that in Arduino it also means to clear RX
 void WiFiClient::flush() {
-    _rxBuffer->flush();
+    int res;
+    size_t a = available(), toRead = 0;
+    if(!a){
+        return;//nothing to flush
+    }
+    uint8_t * buf = (uint8_t *)malloc(WIFI_CLIENT_FLUSH_BUFFER_SIZE);
+    if(!buf){
+        return;//memory error
+    }
+    while(a){
+        toRead = (a>WIFI_CLIENT_FLUSH_BUFFER_SIZE)?WIFI_CLIENT_FLUSH_BUFFER_SIZE:a;
+        res = recv(fd(), buf, toRead, MSG_DONTWAIT);
+        if(res < 0) {
+            log_e("fail on fd %d, errno: %d, \"%s\"", fd(), errno, strerror(errno));
+            stop();
+            break;
+        }
+        a -= res;
+    }
+    free(buf);
 }
 
 uint8_t WiFiClient::connected()