usbnet: remove noisy and hardly useful printk

With turned on hspa modem (Dell 5530 internal card) and activated usb auto
suspend, my system gets up 100 "usbnet_resume has delayed data" per
minute. I didnt noticed any pathological behaviour, so just drop
this message. if any objections, please at least change it to _DEBUG.

Signed-off-by: Christian Samsel <christian.samsel@rwth-aachen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>