Make LinkPropertiesTest backwards compatible

LinkPropertiesTest must be backwards compatible with Q for CTS.

In Q 4 fields were added: DhcpServerAddress, WakeOnLanSupported,
CaptivePortalApiUrl, CaptivePortalData. The new test only tests these
fields on R and above.
testLinkPropertiesParcelable_Q still verifies that there are 14 fields
on Q, so the 4 extra fields can be ignored.

The changes use androidx.core.os.BuildCompat.isAtLeastR(), so
androidx.core_core is added as a dependency to FrameworksNetCommonTests.

Test: atest CtsNetTestCasesLatestSdk:android.net.LinkPropertiesTest
        on Q and R devices
Bug: 150918852
Change-Id: I570efa4eb483a717d4204a18473d02653a69f46d
diff --git a/tests/net/common/Android.bp b/tests/net/common/Android.bp
index e44d460..46d680f 100644
--- a/tests/net/common/Android.bp
+++ b/tests/net/common/Android.bp
@@ -20,6 +20,7 @@
     name: "FrameworksNetCommonTests",
     srcs: ["java/**/*.java", "java/**/*.kt"],
     static_libs: [
+        "androidx.core_core",
         "androidx.test.rules",
         "junit",
         "mockito-target-minus-junit4",