Polling device drivers

Patches for STABLE posted 2 weeks ago on -net

non intrusive, fully backward compatible, no ABI changes
basic driver changes very simple (for well-written drivers at least)

old drivers work unmodified, new drivers self-register for new operating mode.

sysctl net.xorp.polling=1
sysctl net.xorp.poll_burst=10
sysctl net.xorp.poll_in_trap=3

On our test box, peak forwarding rate improved by over 50% while additionally leaving a fully responsive system.