RFR: Make Shenandoah SATB mutex ranks consistent with G1

[Aleksey Shipilev]

On 09/27/2017 04:21 PM, Roman Kennke wrote:
> Apparently, upstream changed the ranks of the SATB mutexes from special to access. We missed to do
> the same. Fix:
> 
> http://cr.openjdk.java.net/~rkennke/satbmutex/webrev.00/

Looks good and consistent with G1 to me.

-Aleksey