linux-kernel-module: move keyring-specific

function afs_set_session_keyring into
if defined(LINUX_KEYRING_SUPPORT)
block. Otherwise compilation fails.

Reviewed-on: http://gerrit.openafs.org/10324
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit b0d75d0687a3436201411384c570448a49a9db15)

Reviewed-on: http://gerrit.openafs.org/10325
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Christof Hanke <christof.hanke@rzg.mpg.de>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
(cherry picked from commit 994da1669293c7c341b5f73fdb7eaebbe530ec90)

Change-Id: I266cb65d60c814bdb333f8193f95b5b61955b544
Reviewed-on: http://gerrit.openafs.org/10331
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Tested-by: Stephan Wiesand <stephan.wiesand@desy.de>