Add NetworkSecurityUnitTests to tethering-mainline-presubmit

Test with connectivity/tethering module only, to catch integration issues with older versions of other modules.

Only the unit test are added to the test_mapping for now. The CTS tests are not compatible with older dessert releases.

The min_sdk_version in the test build target should help preventing the
regressions from b/398885474.

Bug: 397130276
Test: on go/abtd
Change-Id: I215758a34901ff048a8279b4a417ef9f4797db0f
diff --git a/networksecurity/TEST_MAPPING b/networksecurity/TEST_MAPPING
index 448ee84..f75bf9a 100644
--- a/networksecurity/TEST_MAPPING
+++ b/networksecurity/TEST_MAPPING
@@ -1,4 +1,9 @@
 {
+  "tethering-mainline-presubmit": [
+    {
+      "name": "NetworkSecurityUnitTests"
+    }
+  ],
   "presubmit": [
     {
       "name": "CtsNetSecConfigCertificateTransparencyTestCases"