osd: fix feature requirement for mons

These features should be set on the client_messenger, not
cluster_messenger.

Backport: firefly
Signed-off-by: Sage Weil <sage@redhat.com>
Merge pull request #2269 from ceph/wip-osd-mon-feature

osd: fix mon feature requirement

Reviewed-by: Loic Dachary <loic@dachary.org>