Find attached patches that make USB modems just work, fixing this bug.

I have confirmed that at least on x86_64-linux

(service usb-modeswitch-service-type)

works with the default config and that

(service usb-modeswitch-service-type
         (usb-modeswitch-configuration
                              (config-file #f)))

works, passing no config file, leading to different defaults.  Manual
use as described in a comment of the usb-modeswitch package works as
well.


I hope using putenv before wrap-program is OK.  I tried using
computed-file #:options instead, but could not get it to work.

I am uncertain if having paragraphs like this in
modem-manager-service-type and usb-modeswitch-service-type is a good
idea:

     This service is part of ‘%desktop-services’ (*note Desktop
     Services::).


On Sat, May 25, 2019 at 09:42:15PM +0200, pelzflorian (Florian Pelz) wrote:
> Frankly, I am not actually sure if usb_modeswitch_dispatcher is really
> needed for the USB_ModeSwitch service type.

I am sure, it is needed.


> In much earlier (2010)
> versions of USB_ModeSwitch
> (<https://web.archive.org/web/20100921062014/http://draisberghof.de/usb_modeswitch/usb-modeswitch-data-20100826.tar.bz2>)
> the UDEV rules file referred to usb_modeswitch_dispatcher.  It does
> not do so anymore, instead it apparently uses usb_modeswitch directly.
>

There are two different executable files called usb_modeswitch.  The
one used by the UDEV rule runs the dispatcher.


> I will ask in the USB_ModeSwitch forums tomorrow if the dispatcher is
> needed.  I will also ask about an option for specifying the config
> file.  usb_modeswitch has one, usb_modeswitch_dispatcher does not have
> the option.
>

I have not asked.  I will propose the patch after this is commited at
Guix.

Regards,
Florian