Switch from bioq_insert_tail() to bioqdisksort(). When the kernel is

Switch from bioq_insert_tail() to bioqdisksort().  When the kernel is
juggling hundreds of I/O requests the on-disk controllers, which have limited
queue sizes, are unable to completely optimize the accesses.

This seems to make a pretty big difference on the twe device I tested with
when running blogbench on HAMMER, which can approach 1000 simultaniously
queued I/O's.