Currently, the test didn't mock data usage of the month.
Thus, when asserting remaining budget, the calculation
always assumes there is no used data, hence wrong budget
value is expected. See #getRemainingDailyBudget.
This change makes data usage of this month includes the
bytes used today. And adjust the policy limit accordingly.
Test: atest MultipathPolicyTrackerTest
Bug: 204830222
Change-Id: I3ca6505f8d502047485ba3676f16fbc474117cc1
eaa58de991