go/zodb/zeo: Close networkers

xnet.Networker added Close recently and is now required to be explicitly
closed by the user:

go123@01a77bb9

go/zodb/storage/zeo/zeo.go

@@ -406,6 +406,11 @@ func openByURL(ctx context.Context, u *url.URL, opt *zodb.DriverOptions) (_ zodb
 		net  = xnet.NetPlain("unix")
 		addr = u.Path
 	}
+	defer func() {
+		if net != nil {
+			net.Close()
+		}
+	}()
 
 	storageID := "1"
 
@@ -422,6 +427,8 @@ func openByURL(ctx context.Context, u *url.URL, opt *zodb.DriverOptions) (_ zodb
 	if err != nil {
 		return nil, zodb.InvalidTid, err
 	}
+	zlink.closeq = append(zlink.closeq, net)
+	net = nil
 
 	defer func() {
 		if err != nil {

go/zodb/storage/zeo/zeo_test.go

@@ -230,6 +230,9 @@ func TestHandshake(t *testing.T) {
 	withZEOSrv(t, func(t *testing.T, zsrv ZEOSrv) {
 		ctx := context.Background()
 		net := xnet.NetPlain("unix")
+		defer func() {
+			err := net.Close(); X(err)
+		}()
 		zlink, err := dialZLink(ctx, net, zsrv.Addr()); X(err)
 		defer func() {
 			err := zlink.Close(); X(err)

go/zodb/storage/zeo/zrpc.go

@@ -80,6 +80,8 @@ type zLink struct {
 
 	ver string   // protocol version in use (without "Z" or "M" prefix)
 	enc encoding // protocol encoding in use ('Z' or 'M')
+
+	closeq []io.Closer // to be also closed on Close
 }
 
 // zLinkError is returned by zLink operations.
@@ -128,6 +130,12 @@ func (zl *zLink) shutdown(err error) {
 		if err == nil {
 			err = err2
 		}
+		for _, c := range(zl.closeq) {
+			err2 := c.Close()
+			if err == nil {
+				err = err2
+			}
+		}
 		if err != nil {
 			log.Printf("%s", err)
 		}