osdc/Objecter: ignore replies from wrong Connection

Ignore replies on connections we didn't send the request on.  We had a 
previous check that caught most of these cases based on the retry attempt, 
but it is not completely reliable.

Consider:
- send write to A
- A replies with ACK up to 10
- A is killed before committing the write
- A restarts
- B peers with A, at version <10
- resend write to B (no assert_version)
- get ACK from A with uv 10
- B does write with uv != 10

If we do the callback from the first ack, we will expose an incorrect version
to the caller.

Fixes: #7705 Signed-off-by: Sage Weil <sage@inktank.com>