Peers and routers can connect to themselves

[fuzzypixelz]

Describe the bug

It's possible to configure a router or a peer to listen to and to connect to the same endpoint. This breaks pub/sub: all publications are received twice (except the first one for some reason?).

To reproduce

1. Configure an peer or a router with connect/endpoints:["tcp/localhost:10000"] and listen/endpoints:["tcp/localhost:10000"]
2. Start a subscriber on key-expression k
3. Start a publisher on key-expression k with payloads 0, 1, 2, 3, ...

The subscriber will receive 0, 1, 1, 2, 2, 3, 3, ...

System info

• ref: 82869fb