Rework PCEP timers to work on channel

This has the nice property that netty will ensure thread safety, e.g. we
do not have to synchronize channel lifecycle events anymore.

Change-Id: I37ddd71b6cca8210573e767966032885a7678669
Signed-off-by: Robert Varga <rovarga@cisco.com>
Signed-off-by: Dana Kutenicsova <dkutenic@cisco.com>
Merge "Rework PCEP timers to work on channel"