Give CtsHostsideNetworkTests helper apps a min_sdk_version

Missing min_sdk_version will make the helper apps failed to install on
older Android releases.

Bug: 364110022
Test: TH
Change-Id: I2b53d3547d175786574064f9b8b24ea5d302a3ff
diff --git a/tests/cts/hostside/app2/Android.bp b/tests/cts/hostside/app2/Android.bp
index 12ea23b..3dde3ff 100644
--- a/tests/cts/hostside/app2/Android.bp
+++ b/tests/cts/hostside/app2/Android.bp
@@ -36,4 +36,5 @@
         "sts",
     ],
     sdk_version: "test_current",
+    min_sdk_version: "31",
 }
diff --git a/tests/cts/hostside/networkslicingtestapp/Android.bp b/tests/cts/hostside/networkslicingtestapp/Android.bp
index c220000..333195c 100644
--- a/tests/cts/hostside/networkslicingtestapp/Android.bp
+++ b/tests/cts/hostside/networkslicingtestapp/Android.bp
@@ -35,6 +35,7 @@
         "general-tests",
         "sts",
     ],
+    min_sdk_version: "31",
 }
 
 android_test_helper_app {