net: qmi_wwan: fix Gobi device probing

Ignoring interfaces with additional descriptors is not a reliable
method for locating the correct interface on Gobi devices.  There
is at least one device where this method fails:
https://bbs.archlinux.org/viewtopic.php?id=143506



The result is that the AT command port (interface #2) is hidden
from qcserial, preventing traditional serial modem usage:

[   15.562552] qmi_wwan 4-1.6:1.0: cdc-wdm0: USB WDM device
[   15.562691] qmi_wwan 4-1.6:1.0: wwan0: register 'qmi_wwan' at usb-0000:00:1d.0-1.6, Qualcomm Gobi wwan/QMI device, 1e:df:3c:3a:4e:3b
[   15.563383] qmi_wwan: probe of 4-1.6:1.1 failed with error -22
[   15.564189] qmi_wwan 4-1.6:1.2: cdc-wdm1: USB WDM device
[   15.564302] qmi_wwan 4-1.6:1.2: wwan1: register 'qmi_wwan' at usb-0000:00:1d.0-1.6, Qualcomm Gobi wwan/QMI device, 1e:df:3c:3a:4e:3b
[   15.564328] qmi_wwan: probe of 4-1.6:1.3 failed with error -22
[   15.569376] qcserial 4-1.6:1.1: Qualcomm USB modem converter detected
[   15.569440] usb 4-1.6: Qualcomm USB modem converter now attached to ttyUSB0
[   15.570372] qcserial 4-1.6:1.3: Qualcomm USB modem converter detected
[   15.570430] usb 4-1.6: Qualcomm USB modem converter now attached to ttyUSB1

Use static interface numbers taken from the interface map in
qcserial for all Gobi devices instead:

	Gobi 1K USB layout:
	0: serial port (doesn't respond)
	1: serial port (doesn't respond)
	2: AT-capable modem port
	3: QMI/net

	Gobi 2K+ USB layout:
	0: QMI/net
	1: DM/DIAG (use libqcdm from ModemManager for communication)
	2: AT-capable modem port
	3: NMEA

This should be more reliable over all, and will also prevent the
noisy "probe failed" messages.  The whitelisting logic is expected
to be replaced by direct interface number matching in 3.6.

Reported-by: Heinrich Siebmanns (Harvey) <H.Siebmanns@t-online.de>
Cc: <stable@vger.kernel.org> # v3.4: 00001880 USB: qmi_wwan: Make forced int 4 whitelist generic
Cc: <stable@vger.kernel.org> # v3.4: f7142e6c USB: qmi_wwan: Add ZTE (Vodafone) K3520-Z
Cc: <stable@vger.kernel.org> # v3.4
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>