Add tests for pause, resume and stop keepalives.

The tests added verify the following:
1. Stopping the keepalive will cleanup the autoKi.
2. Pausing the keepalive does not cleanup the autoKi and stopping
   a paused keepalive will still call the onStopped callback.
3. A starting error by resuming the keepalive will cleanup the
   autoKi.
4. handleStopAllKeepalives also does the appropriate callback for paused
   keepalives.
5. Stopping a resumed keepalive stops the correct slot when a second
   keepalive is started while the first is paused.

Bug: 281646074
Test: atest FrameworksNetTests
(cherry picked from https://android-review.googlesource.com/q/commit:01d0ef1636dfe27f79530c88d1ee7b939f511055)
Merged-In: I8925fbe40323dc4584a111d0cf31de016525ef41
Change-Id: I8925fbe40323dc4584a111d0cf31de016525ef41
1 file changed