Merge pull request #53 from ESP32Async/compat

Replace `#if ESP_IDF_VERSION_MAJOR < 5` with `#if __has_include(<IPv6Address.h>)`

Author: mathieucarbou

src/AsyncTCP.h

@@ -11,7 +11,7 @@
 
 #ifdef ARDUINO
 #include "IPAddress.h"
-#if ESP_IDF_VERSION_MAJOR < 5
+#if __has_include(<IPv6Address.h>)
 #include "IPv6Address.h"
 #endif
 #endif
@@ -91,7 +91,7 @@ class AsyncClient {
   bool connect(ip_addr_t addr, uint16_t port);
 #ifdef ARDUINO
   bool connect(const IPAddress &ip, uint16_t port);
-#if ESP_IDF_VERSION_MAJOR < 5
+#if __has_include(<IPv6Address.h>)
   bool connect(const IPv6Address &ip, uint16_t port);
 #endif
 #endif
@@ -205,7 +205,7 @@ class AsyncClient {
   ip6_addr_t getRemoteAddress6() const;
   ip6_addr_t getLocalAddress6() const;
 #ifdef ARDUINO
-#if ESP_IDF_VERSION_MAJOR < 5
+#if __has_include(<IPv6Address.h>)
   IPv6Address remoteIP6() const;
   IPv6Address localIP6() const;
 #else
@@ -319,7 +319,7 @@ class AsyncServer {
   AsyncServer(ip_addr_t addr, uint16_t port);
 #ifdef ARDUINO
   AsyncServer(IPAddress addr, uint16_t port);
-#if ESP_IDF_VERSION_MAJOR < 5
+#if __has_include(<IPv6Address.h>)
   AsyncServer(IPv6Address addr, uint16_t port);
 #endif
 #endif