libp2p connectivity check false positive with ipv6?

[lidel]

Extracted from #4, originally reported by @aschmahmann:

AFAICT [this connectivity check (subscribing for EvtLocalReachabilityChanged into network.ReachabilityPublic)] does not work due to a mismatch between the ObsAddrManager and EvtLocalReachabilityChanged as emitted by autonat:

• https://github.com/libp2p/go-libp2p/blob/362e5836f1468aa7f158d5da157c0e99da334d06/p2p/host/autonat/autonat.go#L321-L323 (even a single observation will result in switching to knowing we're public)
• https://github.com/libp2p/go-libp2p/blob/362e5836f1468aa7f158d5da157c0e99da334d06/p2p/protocol/identify/obsaddr.go#L17-L22 (4 address observations are needed to discover a new address)
• But.... we have a public IPv6 address which we can learn about quickly from the OS even though it's not reachable
• So we end up learning we are "public" and having our only public address being an IPv6 one that actually isn't public

This seems like a bug we'd ideally fix within go-libp2p, but maybe I'm missing something
cc @sukunrt @MarcoPolo

[sukunrt]

This will be fixed by libp2p/go-libp2p#2229

To clarify the detail, the AutoNAT Server dials the observed address of the client on the connection(conn.RemoteAddr()) in addition to the ones provided by the client. The observed address manager on the client is not advertising it because it doesn't have enough confidence in the address yet.