operation. Previously ownership was transferred to hardware before
setting address of new RX buffer such that it was possible for
hardware to use wrong RX buffer address.
While here keep compiler from re-ordering instructions by declaring
descriptor members volatile. Memory barriers would do the same job
but volatile is supposed to be cheaper than using memory barriers,
especially on MP systems.
Submitted by: marius
MFC after: 1 week
5ed8e782f9