Fix: test_etcp_simple_traffic race condition and timeout issues

- Moved static variables connection_checked and packet_sent_flag to file scope
  to avoid issues with multiple test runs in the same process
- Added NULL check for uasync_set_timeout return value with error logging
- Added periodic check_packet_received calls in main loop (every 50ms)
  to ensure packet detection even if timeout callback fails

This fixes intermittent test failures where packet was sent but not detected
due to race conditions in timeout handling.

tests/test_etcp_simple_traffic.c

@@ -29,6 +29,10 @@ static uint8_t test_packet_data[PACKET_SIZE];
 static int packet_sent = 0;
 static int packet_received = 0;
 
+// State variables for monitor_and_send (non-static to avoid issues with multiple test runs in same process)
+static int connection_checked = 0;
+static int packet_sent_flag = 0;
+
 // Function to check if connection is established - UPDATED WITH DEBUG
 static int is_connection_established(struct UTUN_INSTANCE* inst) {
     printf("[DEBUG] is_connection_established: Checking instance %p\n", inst);
@@ -198,9 +202,6 @@ static void monitor_and_send(void* arg) {
         return;
     }
     
-    static int connection_checked = 0;
-    static int packet_sent_flag = 0;
-    
     // Check connection
     if (!connection_checked) {
         int server_ready = is_connection_established(server_instance);
@@ -242,7 +243,13 @@ static void monitor_and_send(void* arg) {
     
     // Schedule next check
     if (!test_completed) {
-        packet_timeout_id = uasync_set_timeout(server_instance->ua, 100, NULL, monitor_and_send);
+        void* new_timeout = uasync_set_timeout(server_instance->ua, 100, NULL, monitor_and_send);
+        if (!new_timeout) {
+            DEBUG_ERROR(DEBUG_CATEGORY_ETCP, "monitor_and_send: Failed to set timeout - uasync_set_timeout returned NULL");
+            printf("[ERROR] Failed to set timeout in monitor_and_send\n");
+            fflush(stdout);
+        }
+        packet_timeout_id = new_timeout;
     }
 }
 
@@ -387,10 +394,18 @@ int main() {
 
     int elapsed = 0;
     int poll_interval = 5;
+    int check_counter = 0;
     while (!test_completed && elapsed < TEST_TIMEOUT_MS + 1000) {
         if (ua) uasync_poll(ua, poll_interval);
 
         elapsed += poll_interval;
+        check_counter++;
+
+        // Check for received packet every 10 iterations (every 50ms)
+        // This ensures we check even if the timeout callback doesn't fire
+        if (packet_sent && !packet_received && (check_counter % 10 == 0)) {
+            check_packet_received();
+        }
 
         // Quick exit if packet received
         if (test_completed == 1) {