Mark NetworkStaticLibTestsLib as test for lint

This can avoid VisibleForTesting warnings in tests.

Test: atest NetworkStaticLibTests
Change-Id: If6abc33cf266246aeac22ff4b53cfba386c8979f
diff --git a/staticlibs/tests/unit/Android.bp b/staticlibs/tests/unit/Android.bp
index 031e52f..0dfca57 100644
--- a/staticlibs/tests/unit/Android.bp
+++ b/staticlibs/tests/unit/Android.bp
@@ -33,7 +33,10 @@
         "//packages/modules/Connectivity/Tethering/tests:__subpackages__",
         "//packages/modules/NetworkStack/tests/integration",
     ],
-    lint: { strict_updatability_linting: true },
+    lint: {
+        strict_updatability_linting: true,
+        test: true
+    },
 }
 
 android_test {