[Click] Click scheduling change

[Eddie Kohler]

Hi all,

I've just checked in a refactoring of the way that Click does scheduling.

Previously, each Click thread was "owned" by a particular Router object.
When you changed Routers, the old Router's threads were killed, and new
threads started up.  This happened even on hotswap.

Now, Click threads are "owned" by a persistent object, the Master.  When
kernel Click starts up, it creates N threads, which remain around until you
rmmod the module.  When you change Routers, you change the tasks active in
the Master, but not the kernel threads themselves.

This has a couple benefits.  Hotswaps should be faster and more reliable.
User-level programs can run several routers concurrently by giving them the
same Master.  Also, some kinds of Click configurations will take less CPU
time than they formerly did, because the threads put themselves to sleep as
appropriate.

There may be bugs of course.  Please write in if you see weird behavior.
Eddie