We no longer need to query the plugin manager whether we're checking support for
a specific port, as the ports are now grabbed only once in the MMDevice, and
therefore we ensure that supports check is launched only once in the
PluginManager for that specific port.
Also, we no longer need to query the plugin manager whether we're checking
support for a given device, as the logic to check when all ports of the device
are probed is now maintained internally.
The new `mm_plugin_manager_find_device_support()' will be an async method which
waits for ports to be added in the given `MMDevice'. As soon as all added ports
are probed, the device support check is considered finished.
We chain up the Generic plugin created MMBroadbandModem objects within the
GDBusObjectManagerServer in MMManager, so that they get properly exported in
DBus.
The new mm_plugin_manager_is_finding_port_support() allows to check whether the
Plugin Manager is looking for support in a specific port.
The new mm_plugin_manager_is_checking_device_support() allows to check whether
the Plugin Manager is looking for support in any port of a given device.
The new `mm_plugin_manager_find_port_support()' method requests the Plugin
Manager to iterate over the list of plugins internally handled, launching
supports task for the given port in each of them.
The method is fully asynchronous, and the result can be retrieved with
`mm_plugin_manager_find_port_support_finish()' once the operation is ready.