LU-6401 headers: move swab functions to new header files

LU-6401 headers: move swab functions to new header files

Create headers for pack_generic.c and llog_swab.c
Reference only where needed.

Signed-off-by: Ben Evans <bevans@cray.com>
Change-Id: I0942d2b7e3d60994c43832a94625fa300bac6617
Reviewed-on: http://review.whamcloud.com/16339
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>