[strongSwan-dev] WI: Obsolete kill_daemon

[Martin Willi]

Work-Item: Obsolete kill_daemon

Branch: master

Schedule: 4.4.0

Rationale:
The charon->kill_daemon() has been used by various plugins to shut down
the daemon on critical conditions. Its implementation has always been
tricky, and due to our modularity, has become more and more obsolete.
All invocations of kill_daemon() have been eliminated.

API changes:
The daemon_t.kill_daemon() function has been removed. Use NULL return
values in your plugin instead. To enforce a shut down if a plugin is
unable to load, append a ! to critical plugins in your load directive to
enforce a shutdown if plugin initialization fails.