MFC r271492:
Workaround for receiving Voice Calls using the E1750 dongle from
Huawei. It might appear as if the firmware is allocating memory blocks
according to the USB transfer size and if there is initially a lot of
data, like at the answering machine prompt, it simply dies without any
apparent reason. The simple workaround for this is to force a zero
length packet at hardware level after every 512 bytes of data. This
will force the other side to use smaller memory blocks aswell.

Approved by:    re, gjb