Add a feature flag for USD

USD stands for Unsynchronized Service Discovery. It's a key feature
that allows devices to discover each other directly without needing a
time synchronization. It also enables service discovery and sending
messages using wifi action frames.

Bug: 340878198
Flag: android.net.wifi.flags.usd
Test: build successfuly
Change-Id: I1fd83a8543fb975968998fce98e6fe626951cd42
diff --git a/wifi/wifi.aconfig b/wifi/wifi.aconfig
index 90d13e6..369b809 100644
--- a/wifi/wifi.aconfig
+++ b/wifi/wifi.aconfig
@@ -38,6 +38,15 @@
 }
 
 flag {
+    name: "usd"
+    is_exported: true
+    namespace: "wifi"
+    description: "Unsynchronized Service Discovery"
+    bug: "340878198"
+    is_fixed_read_only: true
+}
+
+flag {
     name: "hotspot_network_connecting_state_for_details_page"
     namespace: "wifi"
     description: "Update getConnectedState in HotspotNetworkEntry so that details page displays correctly."