LU-9859 libcfs: don't save journal_info in dumplog thread.

LU-9859 libcfs: don't save journal_info in dumplog thread.

As this thread is started by kthread, it must have
a clean environment and cannot possibly be in a
filesystem transaction.  So current->journal_info
must be NULL, and preserving it serves no purpose.

Also change libcfs_debug_dumplog_internal() to 'static'
to make it clear that it shouldn't be called from
anywhere but this thread.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Ie863f792b36792600bef4fe778c46e97ebf046c3
Reviewed-on: https://review.whamcloud.com/39294
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>