postcopy: Mask fault addresses to huge page boundary

postcopy: Mask fault addresses to huge page boundary

Currently the fault address received by userfault is rounded to
the host page boundary and a host page is requested from the source.
Use the current RAMBlock page size instead of the general host page
size so that for RAMBlocks backed by huge pages we request the whole
huge page.

Signed-off-by: Dr. David Alan Gilbert <[email protected]>
Reviewed-by: Juan Quintela <[email protected]>
Reviewed-by: Laurent Vivier <[email protected]>
Message-Id: <20170224182844[email protected]>
Signed-off-by: Dr. David Alan Gilbert <[email protected]>