test(edgesec): test "ATTACH" to ap server

Currently, only the OpenWRT test presets of OpenWRT sends an "ATTACH" command to the AP server, which is compiled with GCC.

This causes an issue with code-coverage, because this means that this branch is only covered by code compiled/tested with
GCC, and not via LLVM/Clang. Testing this branch in Clang
should fix this code-coverage issue.

tests/test_edgesec.c

@@ -389,6 +389,11 @@ static void test_edgesec_ap_failure(void **state) {
   {
     int sfd = create_domain_client(NULL);
     assert_return_code(sfd, errno);
+    // should do nothing (just log RECEIVED ATTACH)
+    assert_return_code(write_domain_data_s(sfd, ATTACH_AP_COMMAND,
+                                           strlen(ATTACH_AP_COMMAND),
+                                           socket_path),
+                       errno);
     ssize_t send_invalid_cmd_bytes = write_domain_data_s(
         sfd, "INVALID COMMAND", strlen("INVALID COMMAND"), socket_path);
     close_domain_socket(sfd);