LU-10070 utils: move new SEL find_param fields to end

LU-10070 utils: move new SEL find_param fields to end

Move the new fp_ext_size and fp_ext_size_units fields to the end
of struct find_param so that they don't break the ABI for the
llapi_find() and llapi_getstripe() functions that use it.

Add "unused" fields for the sign and exclude bitfields, so that
it is clear how many more can still be used before we need to
add new fields.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ib15af374774050a9e5b224f7edc7523fdae570c1
Reviewed-on: https://review.whamcloud.com/36554
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Vitaly Fertman <c17818@cray.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>