p2p: close node DB after closing discovery

This fixes a leveldb crash in tests.

Author: fjl

p2p/server.go

@@ -371,7 +371,6 @@ func (srv *Server) Stop() {
 		return
 	}
 	srv.running = false
-	srv.nodedb.Close()
 	if srv.listener != nil {
 		// this unblocks listener Accept
 		srv.listener.Close()
@@ -605,8 +604,9 @@ type dialer interface {
 
 func (srv *Server) run(dialstate dialer) {
 	srv.log.Info("Started P2P networking", "self", srv.localnode.Node())
-
 	defer srv.loopWG.Done()
+	defer srv.nodedb.Close()
+
 	var (
 		peers        = make(map[enode.ID]*Peer)
 		inboundCount = 0