ConnectivityServiceTest: Mark unaudited PendingIntents with FLAG_MUTABLE_UNAUDITED

These PIs need an explicit mutability flag. This temporay flag is being
used to mark these points in code and should be replaced ASAP.
See go/immutable-pendingintents for more context.

Bug: 160794467
Test: TH
Exempt-From-Owner-Approval: noop change
Change-Id: I963d0d737ecbd8ad07577f2fe93ba178419e7a5e