Add extensions to probe message for EC, others

probeMFLN was failing on some connection attempts to servers which only
supported EC based ciphers because it did not include the proper TLS
handshake extensions to list what kinds of ECs it supported.

Add those to the probeMFLN ClientHello message to make probes pass.

Partially fixes esp8266#5996

Author: earlephilhower

libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.cpp

@@ -1221,7 +1221,13 @@ bool WiFiClientSecure::probeMaxFragmentLength(IPAddress ip, uint16_t port, uint1
   //      0xc0, 0x13, // BR_TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
   static const uint8_t clientHelloTail_P[] PROGMEM = {
     0x01, 0x00, // No compression
-    0x00, 0x05, // Extension length
+    0x00, 26 + 14 + 6 +  5, // Extension length
+    0x00, 0x0d, 0x00, 0x16, 0x00, 0x14, 0x04, 0x03, 0x03, 0x03, 0x05, 0x03,
+          0x06, 0x03, 0x02, 0x03, 0x04, 0x01, 0x03, 0x01, 0x05, 0x01, 0x06,
+	  0x01, 0x02, 0x01, // Supported signature algorithms
+    0x00, 0x0a, 0x00, 0x0a, 0x00, 0x08, 0x00, 0x17, 0x00, 0x18, 0x00, 0x19,
+          0x00, 0x1d, // Supported groups
+    0x00, 0x0b, 0x00, 0x02, 0x01, 0x00, // Supported EC formats
     0x00, 0x01, // Max Frag Len
     0x00, 0x01, // len of MaxFragLen
   };