LU-4423 ptlrpc: Fix using smp_processor_id() in preemptible context

LU-4423 ptlrpc: Fix using smp_processor_id() in preemptible context

This warning show up with kernels that enable preemptible
[ 1877.516799] BUG: using smp_processor_id() in preemptible [00000000] code: mount.lustre/14077

Change it to disable preemption around smp_processor_id().

Linux-commit: c369772e78a7383ba4e68673128fe2d6ef2863ee

Fixes: ef94e4d1bb ("LU-8710 ptlrpc: use current CPU instead of hardcoded 0")

Change-Id: If66107f0843c5d0c4bcf874e64a20251fdf9704e
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/35495
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Petros Koutoupis <pkoutoupis@cray.com>
Reviewed-by: Neil Brown <neilb@suse.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>