Update axTLS to 139914f

- Fix occasional software WDT due to lengthy bigint operations
- Implement truly blocking reads as a workaround for half-duplex nature of axTLS

Author: igrr

Diff for: libraries/ESP8266WiFi/src/WiFiClientSecure.cpp

@@ -66,7 +66,7 @@ class SSLContext {
 public:
     SSLContext() {
         if (_ssl_ctx_refcnt == 0) {
-            _ssl_ctx = ssl_ctx_new(SSL_SERVER_VERIFY_LATER | SSL_DEBUG_OPTS | SSL_CONNECT_IN_PARTS, 0);
+            _ssl_ctx = ssl_ctx_new(SSL_SERVER_VERIFY_LATER | SSL_DEBUG_OPTS | SSL_CONNECT_IN_PARTS | SSL_READ_BLOCKING, 0);
         }
         ++_ssl_ctx_refcnt;
     }
@@ -592,3 +592,7 @@ extern "C" void* ax_port_realloc(void* ptr, size_t size, const char* file, int l
 extern "C" void ax_port_free(void* ptr) {
     free(ptr);
 }
+
+extern "C" void ax_wdt_feed() {
+    optimistic_yield(10000);
+}

Diff for: libraries/ESP8266WiFi/src/include/ssl.h

@@ -85,6 +85,7 @@ typedef struct SSL_ SSL;
 #define SSL_DISPLAY_CERTS                       0x00200000
 #define SSL_DISPLAY_RSA                         0x00400000
 #define SSL_CONNECT_IN_PARTS                    0x00800000
+#define SSL_READ_BLOCKING                       0x01000000
 
 /* errors that can be generated */
 #define SSL_OK                                  0