This change starts the periodic hash rescale for all vmem arenas before we load
protocol modules and drivers during boot.  Some drivers relies on heavy vmem
operations (e.g. i40e) and without the periodic vmem hash rescale their
performance could be really bad and the whole boot process would be very slow.

Without this change the boot process on affected machines was stuck for about
30 minutes in the i40e driver.  With the fix the delay is hardly noticeable.

I also confirmed that this change does not intruce any regression on tested
machines.