icE1usb fw: un-configure E1 when altsetting 0 is selected.

So far we started on altsetting 0->1 transition, but we didn't stop
on the inverse 1->0 which typically happens when the host software
(osmo-e1d) stops.

Closes: OS#4676
Change-Id: I8e4817f68d8893ab2dc98fe93ce9a673e209ca63
1 file changed