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

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.

This reverts commit 68add6e814.

This reverts commit a4bea78974.

This reverts commit 3414fd8df8.

This reverts commit 636bd2cd0a.

This reverts commit 7297f04481.

This reverts commit 5ce16b03a1.

This version uses the gPXE driver API rather than the legacy wrapper API.

Convert printf() to DBG(); printf() is not allowed in drivers.

Use generic fields in struct device_description rather than assuming
that the struct device * is contained within a pci_device or
isapnp_device; this assumption is broken when using the undionly
driver.

Add PXENV_UNDI_SET_STATION_ADDRESS.

(i.e. LSB transmitted first on the wire), even though SPI commands and
addresses always have to be big-endian.

structures.

DHCP still broken and #if 0'd out.

Achieved via Perl using:

perl -pi -e 's/pk_buff/io_buffer/g; s/Packet buffer/I\/O buffer/ig; ' \
	-e 's/pkbuff\.h/iobuf.h/g; s/pkb_/iob_/g; s/_pkb/_iob/g; ' \
	-e 's/pkb/iobuf/g; s/PKB/IOB/g;'

ISA 3c509 is currently non-functional, although the EISA (3c509-eisa) and
MCA (3c529) variants should build OK.

None of this code is yet tested.