msg/async: identify client using any: addr

msg/async: identify client using any: addr

The client can speak v1 or v2, so it is misleading to identify it with a v1 or v2
address (it is either).  This avoid some kludgey workarounds.

We also are a bit more precise about what target_addr means.  It is only used by
the client to indicate which of the peer_addrs we are connecting to, or by a
peer to identify which the peer_addrs we *would* reconnect to.

Signed-off-by: Sage Weil <sage@redhat.com>