Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Move de from pci to dev/de

Remove bridge(4) from the tree. if_bridge(4) is a full functional
replacement and has additional features which make it superior.

Discussed on: -arch
Reviewed by: thompsa
X-MFC-after: never (RELENG_6 as transition period)

Unbreak stand-alone build of the de(4) module.

Remove conditional code that has largely rotted that is also not on by
default:
- TULIP_NEED_FASTTIMEOUT - tulip_fasttimeout() wasn't called anywhere
- BIG_PACKET - only worked on i386 anyway
- TULIP_USE_SOFTINTR - doesn't compile and was never updated to handle
new netisr registration
- non-FreeBSD code

Document compile-time switches here as I'm going to yank them from
if_de.c.

Use a consistent style and one much closer to the rest of /usr/src

Convert the de driver into a loadable module. Still missing is an
unload method. Lots of old cruft is removed.

Thanks to WPaul for large clue-injection and debugging services.

Reviewed by: wpaul