Fix return type and comment for up_get

Signed-off-by: Adam C. Emerson <aemerson@linuxbox.com>
Add a general thread fridge

Since all the other thread fridges in the system are used for some
specific purpose, add a queueing worker fridge to accept jobs from
anywhere in ganesha.

Signed-off-by: Adam C. Emerson <aemerson@linuxbox.com>