osd: allow log trimming during recovery

We rely on min_last_complete_ondisk being accurate; as long as we have logs
from that point, the current replicas will be able to safely recovery via
their logs.  Bump the target size, just as we do with degraded.

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Samuel Just <sam.just@inktank.com>