Added test code to configure the interface for IPv4 after DHCP.

cycle.  :)

(apart from the bad UDP checksum).

parsed DHCP responses.

1. Updated UDP send data code\
2. Corrected internet checksum\
3. Moved udp_buffer() and udp_buflen() to udp.c from udp.h

structure, and populating it with options.  This should allow us to
use the same basic options list for both DHCPDISCOVER and DHCPREQUEST,
plus making it much easier to set the non-constant parameters
(e.g. requested IP address) in request packets.

to search through all registered option blocks.

Move some static inlines that are likely to be used frequently into
dhcpopts.c as normal functions, to save space.

derived is a 16-bit big-endian field, but htype is only 8 bits wide.

is a DHCP option" data structures.

We need this code in order to be able to return a DHCP packet to a PXE NBP
which reflects options from our multiple sources (e.g. NVS and DHCP
server).  This is expensive, but necessary.  Having paid this cost, we may
as well try to use the same code to generate our DHCP request packets,
since the process is similar.

DHCP options block from the contents.

encapsulated option; this will be needed for modifications to the options
block.

multiple option sources (e.g. multiple DHCP replies, non-volatile
storage etc.)

- changes made to some constants and macros
- changes made to _curses_screen struct
- identified and removed prototypes for yet more unsupportable functions

transition away from uIP.

Prepared ipv4.c for transition away from uIP.

Kill off the static single net device and move to proper dynamic
registration (which we need with the new device model).

Break the (flawed) assumption that all network-layer protocols can use
ARP; such network-layer protocols (i.e. IPv4) must now register as an ARP
protocol using ARP_NET_PROTOCOL() and provide a single method for checking
the existence of a local network-layer address.

Update rtl8139 driver to instantiate an SPI interface with a three-wire
device attached.

(since SPI bit-bashing will require different delay semantics).

not-yet-updated drivers to at least function.

AoE now uses the retry timer mechanism.