[intel] Poll RX queue if hardware reports RX overflow

[intel] Poll RX queue if hardware reports RX overflow

The Intel NIC emulation in some versions of VMware seems to suffer
from a flaw whereby the Interrupt Cause Register (ICR) fails to assert
the usual "packet received" bit (ICR.RXT0) if a receive overflow
(ICR.RXO) has also occurred.

Work around this flaw by polling for completed descriptors whenever
either ICR.RXT0 or ICR.RXO is asserted.

Reported-by: Miroslav Halas <miroslav.halas@bankofamerica.com>
Debugged-by: Miroslav Halas <miroslav.halas@bankofamerica.com>
Tested-by: Miroslav Halas <miroslav.halas@bankofamerica.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>