client: check for unmounted condition before printing debug output

client: check for unmounted condition before printing debug output

If the filesystem was unmounted before we attempt to call ceph_ll_close
on a Fh, then we can end up tripping over the dereferences in the
debug output. Check for unmounted filesystem first, and only print
the debug info if it's still mounted.

This patch only fixes up ceph_ll_close, which is the only call ganesha
makes after calling ceph_abort_conn. We may need to fix other paths in
the future though if that ever changes.

Tracker: http://tracker.ceph.com/issues/25213
Signed-off-by: Jeff Layton <jlayton@kernel.org>
(cherry picked from commit 3c94f23d3b10928615a0f1381eb758006db84b13)