[ofw] patch: Fix a race in the cl_timer code that caused deadlocks in opensm

[Hefty, Sean]

> One thing to keep in mind is that with the lock to serialize the callback
> threads, you may block threadpool threads that need to run something else,
> so the deadlock might be a side effect of serializing the callbacks with a
> lock.

Okay - the user space implementation of cl_timer uses some system thread pool, which defaults to a maximum of 500 threads.  Deadlock may still be happening at a higher level, but it doesn't seem likely that it would come from the cl_timer implementation.