If host is going to autosuspend function with two interfaces and
if IP packet has arrived in-between of two usbnet_suspend() callbacks,
i.e usbnet_resume() is called in-between, tx data flow is stopped.
When autosuspend timer expires and device is put to autosuspend
again, tx queue is waked up and data can be sent again.
This behavior might be repeated several times in a row.

Tested on Intel/ARM.
Reviewed-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Tested-by: Dmitry Tarnyagin <dmitry.tarnyagin@stericsson.com>
Signed-off-by: Alexey Orishko <alexey.orishko@stericsson.com>
Acked-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>