[hyperv] Receive all VMBus messages in a poll

Allow for elision of transmitted TCP ACKs by handling all received
VMBus messages in each network device poll operation.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[hyperv] Increase TX ring size

Empirical observation suggests that 32 is a sensible size to minimise
the number of deferred packet transmissions without overflowing the
VMBus transmit ring buffer.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[hyperv] Assume that VMBus xfer page ranges correspond to RNDIS messages

The (undocumented) VMBus protocol seems to allow for transfer
page-based packets where the data payload is split into an arbitrary
set of ranges within the transfer page set.

The RNDIS protocol includes a length field within the header of each
message, and it is known from observation that multiple RNDIS messages
can be concatenated into a single VMBus message.

iPXE currently assumes that the transfer page range boundaries are
entirely arbitrary, and uses the RNDIS header length to determine the
RNDIS message boundaries.

Windows Server 2012 R2 generates an RNDIS_INDICATE_STATUS_MSG for an
undocumented and unknown status code (0x40020006) with a malformed
RNDIS header length: the length does not cover the StatusBuffer
portion of the message.  This causes iPXE to report a malformed RNDIS
message and to discard any further RNDIS messages within the same
VMBus message.

The Linux Hyper-V driver assumes that the transfer page range
boundaries correspond to RNDIS message boundaries, and so does not
notice the malformed length field in the RNDIS header.

Match the behaviour of the Linux Hyper-V driver: assume that the
transfer page range boundaries correspond to the RNDIS message
boundaries and ignore the RNDIS header length.  This avoids triggering
the "malformed packet" error and also avoids unnecessary data copying:
since we now have one I/O buffer per RNDIS message, there is no longer
any need to use iob_split().

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[rndis] Ignore start-of-day RNDIS_INDICATE_STATUS_MSG with status 0x40020006

Windows Server 2012 R2 generates an RNDIS_INDICATE_STATUS_MSG with a
status code of 0x4002006.  This status code does not appear to be
documented anywhere within the sphere of human knowledge.

Explicitly ignore this status code in order to avoid unnecessarily
cluttering the display when RNDIS debugging is enabled.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[hyperv] Tidy up debug output

Signed-off-by: Michael Brown <mcb30@ipxe.org>