Add more tests in LinkPropertiesTests.java

Test getAllInterfaceNames(), hasIpv4DefaultRoute(),
hasIpv4DnsServer() and hasIpv6DnsServer().

Bug: 139268426
Bug: 135998869
Bug: 138306002
Test: atest CtsNetTestCasesLatestSdk:android.net.LinkPropertiesTest

Change-Id: I2bae76dc93e7aa02efe25dca4b6e99692c79135a
Merged-In: Ie77dd7eb5c7ecc763c661e8510f9a308e695e77f
(cherry picked from commit 30a56a5c)