[openthread] Use Thread v1.1 instead of v1.2

Bug: b/228617406
Test: Manual verification
Change-Id: Ic27b4b95116c5cd70b99e61f88623153dfb0ecf7
diff --git a/etc/gn/openthread.gni b/etc/gn/openthread.gni
index 28d734d..e34b12d 100644
--- a/etc/gn/openthread.gni
+++ b/etc/gn/openthread.gni
@@ -70,7 +70,7 @@
 if (openthread_enable_core_config_args) {
   declare_args() {
     # Thread version: 1.1, 1.2
-    openthread_config_thread_version = "1.2"
+    openthread_config_thread_version = "1.1"
 
     # Log output: none, debug_uart, app, platform
     openthread_config_log_output = ""