go/p2p: Ensure only server providers advertise themselves

[martintomazic]

Tackles #6262 (comment), see existing slack discussion.

Only hosts that serve p2p protocol should advertise themselves via seed nodes for peer discovery.

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[peternose]

This is not optimal: before that we should check all connected peers via m.host.Peerstore().GetProtocols(remoteID). This way we avoid round-trip to seed nodes. More importantly, we can reuse existing connections and only open a new stream for a new protocol.

Once we connect to a node, we always take into account all its protocols before connecting new ones. See NumProtocolPeers. So when we are out of nodes, we should discover them via seed nodes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.83%. Comparing base (bf911d7) to head (da92e5c).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6270      +/-   ##
==========================================
+ Coverage   64.50%   64.83%   +0.33%     
==========================================
  Files         689      689              
  Lines       67114    67127      +13     
==========================================
+ Hits        43290    43525     +235     
+ Misses      18837    18602     -235     
- Partials     4987     5000      +13     

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[peternose]

^^ not an issue basic host runs identity protocol automatically.

What is identity protocol?

[peternose]

Looks good, will approve once commits are merged.

[martintomazic]

What is identity protocol?

https://github.com/libp2p/go-libp2p/blob/master/p2p/protocol/identify/id.go - responsible for keeping protobook up to date.

This is complementary to your answer #6270 (review) as to how seed nodes are last resource.

[peternose]

This could also be optional as I just saw that we log started advertising when the running thread picks up a new namespace.