Make task priority configurable

Add config option 'CONFIG_ASYNC_TCP_TASK_PRIORITY', which defines what
the tasks' priority is (defaults to 3).

Based on me-no-dev/AsyncTCP#98

Author: avillacis

src/AsyncTCP.cpp

@@ -65,7 +65,7 @@ static bool _start_asyncsock_task(void)
             "asyncTcpSock",
             CONFIG_ASYNC_TCP_STACK,
             NULL,
-            3,                              // <-- TODO: make priority a compile-time parameter
+            CONFIG_ASYNC_TCP_TASK_PRIORITY,
             &_asyncsock_service_task_handle,
             CONFIG_ASYNC_TCP_RUNNING_CORE);
         if (!_asyncsock_service_task_handle) return false;

src/AsyncTCP.h

@@ -47,6 +47,9 @@ extern "C" {
 #ifndef CONFIG_ASYNC_TCP_STACK
 #define CONFIG_ASYNC_TCP_STACK 16384  // 8192 * 2
 #endif
+#ifndef CONFIG_ASYNC_TCP_TASK_PRIORITY
+#define CONFIG_ASYNC_TCP_TASK_PRIORITY 3
+#endif
 
 class AsyncClient;