Add support WiFiClientSecure TCP KeepAlive (esp8266#8940)

* Add support WiFiClientSecure TCP KeepAlive
* Make TCP keepalive and related functions virtual.
* Make TCP keepalive and related functions override.

Fixes esp8266#8939

Author: mobizt

libraries/ESP8266WiFi/src/WiFiClient.h

@@ -107,12 +107,12 @@ class WiFiClient : public Client, public SList<WiFiClient> {
   static void stopAll();
   static void stopAllExcept(WiFiClient * c);
 
-  void     keepAlive (uint16_t idle_sec = TCP_DEFAULT_KEEPALIVE_IDLE_SEC, uint16_t intv_sec = TCP_DEFAULT_KEEPALIVE_INTERVAL_SEC, uint8_t count = TCP_DEFAULT_KEEPALIVE_COUNT);
-  bool     isKeepAliveEnabled () const;
-  uint16_t getKeepAliveIdle () const;
-  uint16_t getKeepAliveInterval () const;
-  uint8_t  getKeepAliveCount () const;
-  void     disableKeepAlive () { keepAlive(0, 0, 0); }
+  virtual void     keepAlive (uint16_t idle_sec = TCP_DEFAULT_KEEPALIVE_IDLE_SEC, uint16_t intv_sec = TCP_DEFAULT_KEEPALIVE_INTERVAL_SEC, uint8_t count = TCP_DEFAULT_KEEPALIVE_COUNT);
+  virtual bool     isKeepAliveEnabled () const;
+  virtual uint16_t getKeepAliveIdle () const;
+  virtual uint16_t getKeepAliveInterval () const;
+  virtual uint8_t  getKeepAliveCount () const;
+  virtual void     disableKeepAlive () { keepAlive(0, 0, 0); }
 
   // default NoDelay=False (Nagle=True=!NoDelay)
   // Nagle is for shortly delaying outgoing data, to send less/bigger packets

libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.h

@@ -357,6 +357,21 @@ class WiFiClientSecure : public WiFiClient {
 
     // consume bytes after use (see peekBuffer)
     virtual void peekConsume (size_t consume) override { return _ctx->peekConsume(consume); }
+  
+    void keepAlive(uint16_t idle_sec = TCP_DEFAULT_KEEPALIVE_IDLE_SEC, uint16_t intv_sec = TCP_DEFAULT_KEEPALIVE_INTERVAL_SEC, uint8_t count = TCP_DEFAULT_KEEPALIVE_COUNT) override
+    {
+      _ctx->keepAlive(idle_sec, intv_sec, count);
+    }
+
+    bool isKeepAliveEnabled() const override { return _ctx->isKeepAliveEnabled(); };
+
+    uint16_t getKeepAliveIdle() const override { return _ctx->getKeepAliveIdle(); };
+
+    uint16_t getKeepAliveInterval() const override { return _ctx->getKeepAliveInterval(); };
+
+    uint8_t getKeepAliveCount() const override { return _ctx->getKeepAliveCount(); };
+
+    void disableKeepAlive() override { _ctx->disableKeepAlive(); };
 
   private:
     std::shared_ptr<WiFiClientSecureCtx> _ctx;