The isc_queue_new() was using dirty tricks to allocate the head and tail
members of the struct aligned to the cacheline. We can now use
isc_mem_get_aligned() to allocate the structure to the cacheline
directly.
Use ISC_OS_CACHELINE_SIZE (64) instead of arbitrary ALIGNMENT (128), one
cacheline size is enough to prevent false sharing.
Cleanup the unused max_threads variable - there was actually no limit on
the maximum number of threads. This was changed a while ago.
