USB: net2280: don't send unwanted zero-length packets

The net2280 driver is too eager to send zero-length packets when
IN tokens are received on ep0.  No such packet should be sent (the
driver should NAK) before the gadget driver has queued the proper
response.  Otherwise deferred responses are impossible.

This patch (as823) makes net2280 avoid sending ZLPs for IN transfers
on ep0 until a response has been submitted, and avoids stalling when an
OUT packet is received before a request has been submitted for an OUT
transfer on ep0.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>