Linux 4.7: Follow key_alloc API change

Linux 4.7: Follow key_alloc API change

Linux v4.7-rc1~124^2~2^2^2~9 adds an eighth optional argument
restrict_link.  The same commit adds a KEY_ALLOC_BYPASS_RESTRICTION
macro, which we test so we can avoid adding another configure test.

Reviewed-on: https://gerrit.openafs.org/12345
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Anders Kaseorg <andersk@mit.edu>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 83a0f2a9ef88e63fbd300fbb436c17ca80c245b4)

Change-Id: I1ba16468888e160fdedf90ff1a9007d90dce9c3b
Reviewed-on: https://gerrit.openafs.org/12348
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Joe Gorse <jhgorse@gmail.com>
Tested-by: Joe Gorse <jhgorse@gmail.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>