Adding multilayered requests to NetworkRequestInfo

Updating NetworkRequestInfo for "multilayered requests" functionality so that
requests can support a network hierarchy. I.e., requests network
with capability A first and if not available, request network with
capability B. This CL is the first step in adding that support by
updating the request object from a single request to a collection.

Bug: 171991028
Test: atest FrameworksNetTests
atest NetworkStackTests
atest FrameworksNetIntegrationTests
atest NetworkStackIntegrationTests
atest CtsNetTestCasesLatestSdk

Change-Id: I64a124802986e4cf4aa7de158c6690fdf9851cb2