Set the SDK version to 29 for networking native tests included in MTS

Here comes a new relocations scheme that isn't compatible with Q
devices after aosp/1673945.
In order to avoid our tests are built with the new scheme, set SDK
version to 29.

Bug: 187905499
Test: forrest, atest
Change-Id: I31f13e2b95bacdca4c1897742cada2da169a89fd
diff --git a/tests/cts/net/native/dns/Android.bp b/tests/cts/net/native/dns/Android.bp
index 5e9af8e..434e529 100644
--- a/tests/cts/net/native/dns/Android.bp
+++ b/tests/cts/net/native/dns/Android.bp
@@ -24,6 +24,8 @@
         "liblog",
         "libutils",
     ],
+    // To be compatible with Q devices, the min_sdk_version must be 29.
+    min_sdk_version: "29",
 }
 
 cc_test {