net: qmi_wwan: add ZTE MF880

The driver description files gives these names to the vendor specific
functions on this modem:

 diag: VID_19D2&PID_0284&MI_00
 nmea: VID_19D2&PID_0284&MI_01
 at:   VID_19D2&PID_0284&MI_02
 mdm:  VID_19D2&PID_0284&MI_03
 net:  VID_19D2&PID_0284&MI_04

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>