Cleanups for e1000.c.

supply options.

PXENV_GET_CACHED_INFO.  If we dont do this, Altiris' NBP screws up; it
relies on being able to grab pointers to each of the three packets and
then read them at will later.

s_PXENV_GET_CACHED_INFO, because this field doesn't exist in earlier
versions of the PXE spec, and some callers don't allocate space for it.

also avoid waiting for ProxyDHCP offers).

Also reduce the ProxyDHCP timeout, because it's already irritating me.

I have successfully booted DOS via iSCSI and PXELINUX via TFTP with this
version of the e1000 driver.

implemented smbios_get_uuid().

potentially exorbitant amounts of stack space.

There may still be an issue with memory handling, since it seems to
die ungracefully when ARP packets come in after loading a kernel.
Something to debug.

autonegotiation still needs work.  receive is not working yet.

needing to know the gPXE internal ROM name.

It is likely we will rename e1000_main to e1000 when the new e1000 driver is debugged.

We didn't specify values for MaxRecvDataSegmentLength and
MaxBurstLength (to save space, since we were happy with the
RFC-defined default values of 8kB and 256kB respectively).  However,
the OpenSolaris target (incorrectly) assumes default values of zero
for these parameters.

The upshot was that the OpenSolaris target would get stuck in an
endless loop trying to send us the first 512-byte sector, zero bytes
at a time, and would eventually run out of memory and core-dump.

Fixed by explicitly specifying the default values for these two
parameters.

allowing any space for this, which makes it surprising that bzImage
loading ever worked.

memory map.  (We achieve this by setting CF on the last entry if it is
zero-length; this avoids the need to look ahead to see at each entry
if the *next* entry would be both the last entry and zero-length).

This fixes the "0kB base memory" error message upon starting Windows
2003 on a SunFire X2100.

memory map.  (We achieve this by setting CF on the last entry if it is
zero-length; this avoids the need to look ahead to see at each entry
if the *next* entry would be both the last entry and zero-length).

This fixes the "0kB base memory" error message upon starting Windows
2003 on a SunFire X2100.

packet, to work around the problem whereby small TX rings get backed
up because we haven't yet poll()ed for TX completions.