Give CtsHostsideNetworkTests helper apps a min_sdk_version.

This allows them to run on older Android releases.

Fix: 358007993
Test: test-only change
Change-Id: I3c1e7eb6a3aeb53ae9bb2dadb5827d5987755905
diff --git a/tests/cts/hostside/app/Android.bp b/tests/cts/hostside/app/Android.bp
index 919e025..798cf98 100644
--- a/tests/cts/hostside/app/Android.bp
+++ b/tests/cts/hostside/app/Android.bp
@@ -44,6 +44,7 @@
         "general-tests",
         "sts",
     ],
+    min_sdk_version: "31",
 }
 
 android_test_helper_app {