osd: do not require EC feature bit from clients.

I just find it confusing if we say that the mask is not impacted by the entity_type we pass in, and I see benefits to doing it the other way. For instance, if we had it impacted by entity_type, we could do things based on the mask like identify features which the cluster doesn't currently require, but which it might after a config change, and warn clients if they don't support those.
Whereas, what good does it do us to have the mask be constant across entity_types?