libqmi-glib,device: expected data format and wwan iface are qmi_wwan specific

The APIs that get/set the expected data format in the kernel, as well as the one to guess the network interface name for a given QMI control port are specific to the qmi_wwan driver, so explicitly say that in the documentation API and make sure these APIs don't succeed with hardcoded values for other setups.

E.g. the qmi_device_get_wwan_iface() should not return a hardcoded 'rmnet_data0' that may not even exist in the system as associated wwan iface name.

The API documentation for all qmi_device_get_wwan_iface(), qmi_device_get_expected_data_format() and qmi_device_set_expected_data_format() now explicitly indicate that these methods will are only applicable when using the qmi_wwan kernel driver.