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