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>
Reviewed-by: Samuel Just <sam.just@inktank.com>