session: Add a list of pending connect/disconnect actions

session: Add a list of pending connect/disconnect actions

deselect_service() and select_offline_service() want to clear
up the session state machinery by setting up a zero second
timeout function thereby letting the main loop run once through
all waiting actions. Unfortunately, if a service is being
removed meantime, the service structure stored in the timeout
functions will become invalid.

This is fixed by adding a list of pending connect/disconnect
actions per struct service_entry and cancelling all of them
if the service is removed.

Fixes BMC#22879