Currently, ConnectivityService decides the request type by
whether NetworkCapabilities is null when handling request
network. However, to fulfill the need of firing background
request via ConnectivityManager in the follow-up patches,
the request type is needed to pass into ConnectivityService.
This change also make ConnectivityService utilizes the passed
request type.
Test: atest ConnectivityManagerTest#testRequestType
Bug: 175662146
Change-Id: I3bc172bca1217c8020db45057a621d0745d43b3c
ad0107998f