dscpPolicyTest: make it actually test caching

Test: TreeHugger, atest CtsNetTestCases:android.net.cts.DscpPolicyTest
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I4164732ed5545c43fd02cbb9d9dae57966241ab8
1 file changed