network: add default MinPeers

If there is nothing specified in the configuration, set it to some reasonable
value.

pkg/network/server.go

@@ -18,6 +18,7 @@ import (
 
 const (
 	// peer numbers are arbitrary at the moment.
+	defaultMinPeers = 5
 	maxPeers        = 20
 	maxBlockBatch   = 200
 	maxAddrsToSend  = 200
@@ -76,6 +77,14 @@ func NewServer(config ServerConfig, chain core.Blockchainer) *Server {
 		peers:        make(map[Peer]bool),
 	}
 
+	if s.MinPeers <= 0 {
+		log.WithFields(log.Fields{
+			"MinPeers configured": s.MinPeers,
+			"MinPeers actual":     defaultMinPeers,
+		}).Info("bad MinPeers configured, using the default value")
+		s.MinPeers = defaultMinPeers
+	}
+
 	s.transport = NewTCPTransport(s, fmt.Sprintf(":%d", config.ListenTCP))
 	s.discovery = NewDefaultDiscovery(
 		s.DialTimeout,