LINUX: Copy session keys to parent in SetToken

LINUX: Copy session keys to parent in SetToken

Commit 48589b5d (Linux: Restore aklog -setpag functionality for kernel
2.6.32+) added code to SetToken() to copy our session keyring to the
parent process, in order to implement -setpag functionality. But this
was removed from SetToken() in commit 1a6d4c16 (Linux: fix aklog
-setpag to work with ktc_SetTokenEx), when the same code was moved to
ktc_SetTokenEx().

Add this code back to SetTokens(), so -setpag functionality can work
again with utilities that use older functions like ktc_SetToken, like
'klog'.

Change-Id: I68c9bf2e19783ea6f84b4c5ebf2ef188d1d8d6ad
Reviewed-on: https://gerrit.openafs.org/14146
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>