LU-2590 obdclass: correct swab lov_mds_md

For caller's convenience, the 2nd parameter of obd_free_diskmd()
could be host endianness, it needs swab to LE if necessary, while just
lov_mds_md header needs it for figuring out how much memory needs to
be freed.

Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Change-Id: I537e83b56b4be6e08a7431bfda1de71efefa33ee
Patch-Set: 2