LU-2221 ptlrpc: kerberos support for kernel>=2.6.24

LU-2221 ptlrpc: kerberos support for kernel>=2.6.24

Since kernel 2.6.24 the scatterlist struct has no field "page".
Then related Lustre kerberos code cannot work anymore.

So do not access scatterlist::page directly, instead, use the
scatterlist functions sg_set_page and sg_assign_page.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Signed-off-by: Thomas Stibor <thomas@stibor.net>
Change-Id: I446925bb42c1e018a55a69948383c8f71976f1fa
Reviewed-on: http://review.whamcloud.com/4394
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>