ctl interrupt priorities

Once upon a time, a long time ago there was information about interrupt priorities when using ctl.  On some architectures, you need to use the ctl_set_priority() function to ensure that the MSB is set.  There isn't really anything documented about this.  It would be nice to add this information to the ctl_enter_isr() sections.  I just had a new employee get an error due to this.  He had read the ctl documentation but this wasn't listed.  I tried to find it and couldn't either.