LU-4975 ofd: documenting the ofd_fs.c

LU-4975 ofd: documenting the ofd_fs.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_fs.c file and add
function comment blocks to all functions in it.
Couple tiny helpers are moved inside caller code because they are
called just from one place and contains few lines of code.
This patch changes cfs_list_t->struct list_head also in several
places.

Signed-off-by: Mikhail Pershin <mike.pershin@intel.com>
Change-Id: Ifa231f941c80c98bb9a0c20bdd56e1ae379f496a
Reviewed-on: http://review.whamcloud.com/10417
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>