Add new Reload D-Bus command to reload NetworkManager configuration.
For now, this is like sending SIGHUP to the process. There are several
advantages here:
- it is guarded via PolicyKit authentication while signals
can only be sent by root.
- the user can wait for the reload to be complete instead of sending
an asynchronous signal. For now, we operation completes after
nm_config_reload() returns, but later we could delay the response
further until specific parts are fully reloaded.
- SIGHUP reloads everything including re-reading configuration from
disk while SIGUSR1 reloads just certain parts such as writing out DNS
configuration anew.
Now, the Reload command has a flags argument which is more granular
in selecting parts which are to be reloaded. For example, via
signals the user can:
1) send SIGUSR1: this writes out the DNS configuration to
resolv.conf and possibly reloads other parts without
re-reading configuration and without restarting the DNS plugin.
2) send SIGHUP: this reloads configuration from disk,
writes out resolv.conf and restarts the DNS plugin.
There is no way, to only restart the DNS plugin without also reloading
everything else.