b=22755 more grant fixes

i=oleg
i=wangdi

- filter_preprw_write() should check for OBD_FL_SHRINK_GRANT in o_flags instead of
  o_valid;
- The grant shrink code should not use o_flags w/o setting OBD_MD_FLFLAGS since
  o_flags can be legitimately reset if OBD_MD_FLFLAGS (e.g. it is done in the
  checksum code);
- add OBD_FL_MMAP to wiretest & wirecheck