Kill off use of etherboot.h outside drivers/net.

optimisation of only trying to do so when necessary.

number of (potentially very slow) gateA20_set operations.

Die with a fatal error if we are unable to set gate A20; if this fails
then we are bound to experience memory corruption at a later stage,
and I'd prefer to pick it up early.

in tcp_rx_data().

Clarify comments on discarding duplicate or out-of-order data.

the UNDI stack.

Ignore obviously invalid length combinations (as returned by
e.g. VMWare's PXE stack).

Limit to one packet per poll to avoid memory exhaustion.

Always send EOI; do not chain to BIOS's default interrupt handler.
They are just too unpredictable; at least VMware's seems to kill the
machine if you go anywhere near it.

Disable interrupts after return from PXENV_UNDI_ISR, just in case some
dumb PXE stack enables them.

which respond to close with a reopen() (e.g. iSCSI).

INT 13,08 : read number of drives from 40:75
INT 13,15 : do nothing
all others : restore original value of %dl

on failure).

SCSI interface not yet implemented.

implemented; should be done at some point.)

applied.

obtained via xfer_window().

xfer_window() function, which can return a scalar rather than a
boolean.

This reverts commit fc5f6c9de2.

Reverted commit breaks the much more common case of changing the debug
options in subsequent builds without any code changes.

safe dropping of the netdev ref by the driver while other refs still
exist.

Add netdev_irq() method.  Net device open()/close() methods should no
longer enable or disable IRQs.

Remove rx_quota; it wasn't used anywhere and added too much complexity
to implementing correct interrupt-masking behaviour in pxe_undi.c.

This reverts commit 3487640397.