New device_polling algorithm

[Ryan Stone]

A couple of things that I forgot:

- Note that DEVICE_POLLING is not included in GENERIC.  You'll have to
add the following to your kernel config to get polling support:

options DEVICE_POLLING

- you can enable polling on a interface with ifconfig(provided the
driver supports polling)

ifconfig <interface name> polling

- Thanks to attilio@ and emaste@ for reviewing the patch

Ryan