Linux: 3.1: update RCU path walking detection in permission i_op

Linux: 3.1: update RCU path walking detection in permission i_op

The permission() inode operation changed again with kernel 3.1,
back to the form it had before 2.6.38.  This compiles fine,
but is missing the new way of detecting when we get called in
RCU path walking mode, resulting in system hangs.

Change-Id: I9a9a0c13aa3b35d8fe2bd592e2bca8187eacacc5
Reviewed-on: http://gerrit.openafs.org/5740
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>