LU-4975 ofd: documenting ofd_io.c

LU-4975 ofd: documenting ofd_io.c

Fix up GPL header block to reference proper GPLv2 license URL.
Remove mention of contacting Sun, since they don't exist anymore.
Add introductory comment block for the ofd_io.c file and add
function comment blocks to all functions in it.

Signed-off-by: Mikhail Pershin <mike.pershin@intel.com>
Change-Id: Ic45e8a53f6df127c815f332ef2f5e219506727aa
Reviewed-on: http://review.whamcloud.com/11156
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>