fix: don't create libp2p metrics twice [fixes NET-348]

[kmd-fl]

Using only Arc without Mutex is okay, since the metrics are atomic/mutexed inside themselves.

[linear]

NET-348 rust-peer libp2p metrics duplicated

docker run --rm -p 7777:7777 -p 18080:18080 fluencelabs/rust-peer:0.1.8 --local

Trigger metric increase

curl localhost:7777

Check metrics

curl -Ss localhost:18080/metrics | grep connections_incoming_total

Result is

libp2p_swarm_connections_incoming_total 0
libp2p_swarm_connections_incoming_total 1

Not critical, as correct metric comes last and monitoring database discards the double. But still better to be fixed