b=22755 more shrink grant fixes

b=22755 more shrink grant fixes

i=di.wang
i=oleg.drokin

- 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);
- OBD_FL_MMAP is added to wiretest & wirecheck