Do best effort network estimate calculation.

Ignore invalid negative values in the network payload estimate
calculations and use known/available values to get a best effort
estimate of the total payload size.

Bug: 253665015
Bug: 255828754
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/job
Test: atest frameworks/base/services/tests/mockingservicestests/src/com/android/server/job
Change-Id: Ie986ac8a4b46a920c6d57b6925e72f8d62e1ce68