Don't enable interrupts before we call sched_throw(). Interrupts
are expected to be disabled by virtue of md_spinlock_count==1
assumed to hold.
Use the correct map to setup the jumbo RX ring entry.
Use the right operator to get the bit shift form the entry. We were
mistakenly clearing bit 0 in the corresponding 64-bit integral.
Add PROCDESC
Fix busdma_md_unload() to recursively call devices up the
device tree. When we map we start at the root and recurse
down to the leaf device. When we unmap, we go the reverse
direction.

This fix actually has us call the unmap function of the
PCI bridge, which means we now free up I/O MMU mappings.

This and previous few commits were all done from the Altix
itself. Looking good...
Use an I/O MMU page size of 4KB when the kernel uses a page size less
than 16KB. Use a 16KB I/O MMU page size otherwise.