net: usb: Fix premature auto suspend on Rx data path

usbnet driver does not prevent auto suspend while submitting
the URB on rx data path. This causes the usb device to go to low power
mode in the middle of the downlink data transfer as the auto suspend
timer does not get reset by the driver while submitting the URB and
it expires.

Change-Id: Ibd3ac709e7103eb3df91ce3318dba6da4e551366
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>