paxos: set last_committed in share_state()
paxos: set last_committed in share_state()

It wasn't getting set for LAST message, which broke recovery somewhat.

Broken by 8e76c5a1d827e01f77149245679bd00ba27120e0.

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph