fix: use pre-defined relays for autorelay

Unfortunately, we don't currently have any way to pick out good relays from bad.
That means we keep searching, trying bad relays, searching some more, trying
_the same relays_, etc. until we randomly find 3 good stable relays. In
practice, this means we just keep searching forever and keep thrashing the DHT.

see libp2p/go-libp2p#694

core/node/libp2p/relay.go

@@ -21,4 +21,4 @@ func Relay(disable, enableHop bool) func() (opts Libp2pOpts, err error) {
 	}
 }
 
-var AutoRelay = simpleOpt(libp2p.EnableAutoRelay())
+var AutoRelay = simpleOpt(libp2p.ChainOptions(libp2p.EnableAutoRelay(), libp2p.DefaultStaticRelays()))

go.sum

@@ -354,8 +354,8 @@ github.com/libp2p/go-libp2p v0.4.0 h1:nV2q3fdhL80OWtPyBrsoWKcw32qC4TbbR+iGjEOMRa
 github.com/libp2p/go-libp2p v0.4.0/go.mod h1:9EsEIf9p2UDuwtPd0DwJsAl0qXVxgAnuDGRvHbfATfI=
 github.com/libp2p/go-libp2p v0.4.2 h1:p0cthB0jDNHO4gH2HzS8/nAMMXbfUlFHs0jwZ4U+F2g=
 github.com/libp2p/go-libp2p v0.4.2/go.mod h1:MNmgUxUw5pMsdOzMlT0EE7oKjRasl+WyVwM0IBlpKgQ=
-github.com/libp2p/go-libp2p v0.5.0 h1:/nnb5mc2TK6TwknECsWIkfCwMTHv0AXbvzxlnVivfeg=
-github.com/libp2p/go-libp2p v0.5.0/go.mod h1:Os7a5Z3B+ErF4v7zgIJ7nBHNu2LYt8ZMLkTQUB3G/wA=
+github.com/libp2p/go-libp2p v0.5.1 h1:kZ9jg+2B9IIptRcltBHKBrQdhXNNSrjCoztvrMx7tqI=
+github.com/libp2p/go-libp2p v0.5.1/go.mod h1:Os7a5Z3B+ErF4v7zgIJ7nBHNu2LYt8ZMLkTQUB3G/wA=
 github.com/libp2p/go-libp2p-autonat v0.0.2/go.mod h1:fs71q5Xk+pdnKU014o2iq1RhMs9/PMaG5zXRFNnIIT4=
 github.com/libp2p/go-libp2p-autonat v0.0.6/go.mod h1:uZneLdOkZHro35xIhpbtTzLlgYturpu4J5+0cZK3MqE=
 github.com/libp2p/go-libp2p-autonat v0.1.0 h1:aCWAu43Ri4nU0ZPO7NyLzUvvfqd0nE3dX0R/ZGYVgOU=