Linux 4.4: key_payload has no member 'value'

Linux 4.4: key_payload has no member 'value'

In Linux 4.4 (146aa8b1453bd8f1ff2304ffb71b4ee0eb9acdcc) type-specific and
payload data have been merged. The payload is now accessed directly and has
no 'value' member anymore.

FIXES 132677

Change-Id: Id26c40c80314a0087ecc0735029412787058ef07
Reviewed-on: https://gerrit.openafs.org/12169
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Tested-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>