Dont discover self

[jacobheun]

Original issue: https://github.com/libp2p/js-libp2p-switch/issues/331.

On peer discovery, if the peer happens to be us, we should avoid adding ourselves to the PeerBook and emitting a peer:discovery event.

[mkg20001]

Additionally maybe log a warning like "WARN: Discovery module $NAME caused this peer to discover itself. This is a bug and should be reported at $URL" (url could be read from package.json, as npmjs.com currently does)
The warning should be shown just once. possibly also print a line to debug log everytime this happens so user knows how frequently this is occurring

[jacobheun]

Additionally maybe log a warning like "WARN: Discovery module $NAME caused this peer to discover itself.

While I think this is valuable I think having the warning code always be present might be unncessary. I think if we log an error we'll at least have the stack trace of where it came from and the frequency it happens. Additionally I think the right thing to do would be to add self discovery tests to https://github.com/libp2p/interface-peer-discovery (along with the other tests it should have), and get that added to each of the discovery service test suites. @mkg20001 what do you think about that approach?

[mkg20001]

@jacobheun Tests sound great, should also be mandatory. About log: Put it in debug log. That should be enough, so developers know it's happening and can report bugs

[jacobheun]

About log: Put it in debug log.

I added the error to debug for libp2p:error in #357.

Tests sound great, should also be mandatory.

I'll create an issue over at interface-discovery to track this.