Bug fix - mprotect may be called with wrong flags
Query si_flags instead of attributes when determining whether a layout
entry should be readable/writable or not accessible. The current code
magically works because all layout entries that should be marked R/W
will have a non-zero value for attributes since added pages are marked
with either ADD_EXTEND_PAGE or ADD_EXTEND_PAGE.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>