mds: raise health warning if client lacks feature for root_squash

mds: raise health warning if client lacks feature for root_squash

Rather than evict all clients lacking this feature bit, raise a health error
that pushes the administrator to address it. This avoids the surprise of having
all affected clients suddenly evicted in the cluster.

Fixes: https://tracker.ceph.com/issues/65733
Fixes: 954ed30
Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>