enableAutoNAT ran both the AutoNAT v2 client (this host checks its own
reachability) and the server (this host answers other peers' checks
with a dial-back). A host that is usually behind NAT, such as a phone,
is a poor server: each check costs it a dial-back, and a dial-back that
fails because of the phone's own network tells the other peer that its
address is unreachable.

Libp2p.autoNATv2Server(false), or Config.enableAutoNATv2Server = false,
keeps the client and removes the server; the host then makes no
dial-back host. AutoNATv2Impl takes enableServer. The default does not
change: the server runs, as in go-libp2p.

Release 4.2.0.