Stop ConnectivityController from processing non-network jobs.

Jobs that don't require network won't have a NetworkRequest object, so
trying to process them fully in ConnectivityController will lead to
NPEs.

Bug: 148218476
Test: atest com.android.server.job.controllers.ConnectivityControllerTest#testRestrictedJobTracking
Change-Id: Ibcb4162c19fc97d09f860bb1732e465de5c8374e