[wlanloader] WLAN loader plugin

Apparently Android by default resets the WLAN driver after
every use of WLAN hotspot. To make it easier to work with android
kernels whose WLAN module depends on this kind of reset service,
this plugin will imitate that behavior by reloading the
kernel module via a systemd service after each use of
WLAN hotspot.

If you want to utilize this plugin, please add a systemd system
service that is named "wlan-module-load.service" to your adaptation
project. The service should modprobe the wlan kernel module at
ExecStart, and rmmod it at ExecStop.

If the systemd service is not present in the system, the plugin will
not do anything.

Signed-off-by: Kalle Jokiniemi <kalle.jokiniemi@jolla.com>
The loader_in_use and bound variables seem to overlap -> might just use one of them. My suggestion

1) remove 'loader_in_use' variable (no real harm in having it, so this is not necessary)
2) in any case do not make dsme_dbus_unbind_signals() call at disconnect depend on loader_in_use

Note that dsme_dbus_unbind_signals() is a dummy with FIXME ... only the boolean gets toggled.
But since dsme will nowadays exit if it gets disconnected there should be no risk of multiple
signal listener registrations via connect/disconnect/connect cycles (and the loader_in_use would
not protect from them anyway).