libnetwork/diagnostic: EnableDiagnostic(): use net.JoinHostPort

Use net.JoinHostPort to account for IPv6 addresses.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit a33d1f9a7c)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

libnetwork/diagnostic/server.go

@@ -4,7 +4,9 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"net"
 	"net/http"
+	"strconv"
 	"sync"
 	"sync/atomic"
 
@@ -91,7 +93,10 @@ func (s *Server) EnableDiagnostic(ip string, port int) {
 	}
 
 	logrus.Infof("Starting the diagnostic server listening on %d for commands", port)
-	srv := &http.Server{Addr: fmt.Sprintf("%s:%d", ip, port), Handler: s}
+	srv := &http.Server{
+		Addr:    net.JoinHostPort(ip, strconv.Itoa(port)),
+		Handler: s,
+	}
 	s.srv = srv
 	s.enable = 1
 	go func(n *Server) {