boot - Hack workarounds for chromebook 'SeaBIOS' issues

* The google seabios hack to boot legacy-mode only reports 16MB of extended
  memory.  For now, enforce a minimum of 64MB.

  This was preventing the loader from being able to load the kernel+modules.

* Fix a bug in biosdisk.c to force bounce buffers if the target buffer
  is beyond the segment address limit, in addition to checking for
  64KB boundary crossings.
kernel - if_rue (old usb stack) fixes

* Fix the more obvious lockups and locking issues with if_rue (a usb
  ethernet device).

* Still breaks when you run ifconfig sometimes (locks up).
netmap: more porting; undo some mistakes

Probably adds new issues, too.  There's some VM magic,
cdev_t adaption and a couple of network internals left.