Add min_sdk_version:R to updatable apexes

APEXes introduced in R need to set min_sdk_version to ensure that they
are built against correct version(30 or R) of stubs (libc/liblog/...).

Bug: 152655956
Test: /vendor/google/build/build_mainline_modules.sh
Change-Id: I4a893c34b09334eea124266287301e479b9e8a59
diff --git a/apex/sdkextensions/Android.bp b/apex/sdkextensions/Android.bp
index 322d5e1..fc26e08 100644
--- a/apex/sdkextensions/Android.bp
+++ b/apex/sdkextensions/Android.bp
@@ -27,6 +27,7 @@
 apex_defaults {
     name: "com.android.sdkext-defaults",
     updatable: true,
+    min_sdk_version: "R",
     java_libs: [ "framework-sdkextensions" ],
     prebuilts: [
         "derive_sdk.rc",