Update pixel-sepolicy to allow the wifi_ext AIDL service.

Bug: 205044134
Test: Start wifi on an Oriole device using both the
      HIDL and AIDL versions of wifi_ext.
Change-Id: I43b224f5c592200c1eb24c93d14a0e8f7e3f5497
diff --git a/wifi_ext/service_contexts b/wifi_ext/service_contexts
new file mode 100644
index 0000000..8f782df
--- /dev/null
+++ b/wifi_ext/service_contexts
@@ -0,0 +1,2 @@
+# Wifi
+vendor.google.wifi_ext.IWifiExt/default  u:object_r:hal_wifi_ext_service:s0