Today, when NetworkManager quits after SIGTERM, it synchronously performs some cleanup actions and quits. That has problems, and in the future the shutdown needs to be reworked as described in the TODO file.
While the FIXME(shutdown) work is not yet done, we already have various API and things in place, for those future changes (nm_shutdown_wait_obj_*() and NM_SHUTDOWN_TIMEOUT_*).
This branch cleans up some things related to NM_SHUTDOWN_TIMEOUT* macros. In particular, the shutdown grace period gets incremented to 5 seconds, so it can also cover the time it takes before killing pppd.
There is no actual change in behavior in this branch, instead, it is a preparation for the future work.