acer-wmi: check the existence of internal 3G device when set capability

That will be better to check the existence of internal 3G device when
we set threeg capability and generate killswitch for threeg. It can
avoid userland access 3G rfkill but the machine doesn't have internal
3G device.

Reference: bko#32862
	https://bugzilla.kernel.org/show_bug.cgi?id=32862



Tested on Acer Aspire 8930G, Acer Travelmate 8572

Tested-by: Hector Martin <hector@marcansoft.com>
Cc: Carlos Corbacho <carlos@strangeworlds.co.uk>
Cc: Matthew Garrett <mjg@redhat.com>
Cc: Dmitry Torokhov <dtor@mail.ru>
Cc: Corentin Chary <corentincj@iksaif.net>
Cc: Thomas Renninger <trenn@suse.de>
Signed-off-by: Lee, Chun-Yi <jlee@novell.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>