Fix nascent timer never get removed

By design, the nascent timer will be removed after a network
satisfied first request. However, this never happens.
Because the mInactive is false when that happens, so isNascent
is never true.

Furthermore, when removing a nascent timer, the inactivity
state can never be updated since no condition in the
updateInactivityState will be met to update the state correctly.

Thus, update inactive state accordingly when adding/removing the
nascent timer.

Test: TH
Bug: 184227264
Ignore-AOSP-First: prevent merge conflict
Change-Id: I4c1521b6e0ef68ac489771a2ab6b09ef3e381577