improve number of peers metric (#4527)

Signed-off-by: Stefan <stefan.pingel@consensys.net>

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/manager/EthPeers.java

@@ -94,6 +94,11 @@ public class EthPeers {
         "pending_peer_requests_current",
         "Number of peer requests currently pending because peers are busy",
         pendingRequests::size);
+    metricsSystem.createIntegerGauge(
+        BesuMetricCategory.ETHEREUM,
+        "peer_count",
+        "The current number of peers connected",
+        () -> (int) streamAvailablePeers().count());
   }
 
   public void registerConnection(

ethereum/p2p/src/main/java/org/hyperledger/besu/ethereum/p2p/rlpx/RlpxAgent.java

@@ -111,11 +111,6 @@ public class RlpxAgent {
         metricsSystem.createCounter(
             BesuMetricCategory.PEERS, "connected_total", "Total number of peers connected");
 
-    metricsSystem.createIntegerGauge(
-        BesuMetricCategory.ETHEREUM,
-        "peer_count",
-        "The current number of peers connected",
-        this::getConnectionCount);
     metricsSystem.createIntegerGauge(
         BesuMetricCategory.ETHEREUM,
         "peer_limit",