cmd/dockerd: explicitly ignore unchecked errors (errcheck)

```
cmd/dockerd/config.go:50:18: Error return value of `flags.MarkHidden` is not checked (errcheck)
cmd/dockerd/config.go:55:22: Error return value of `flags.MarkDeprecated` is not checked (errcheck)
cmd/dockerd/config.go:78:18: Error return value of `flags.MarkHidden` is not checked (errcheck)
```

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cmd/dockerd/config.go

@@ -47,12 +47,12 @@ func installCommonConfigFlags(conf *config.Config, flags *pflag.FlagSet) error {
 
 	// "--graph" is "soft-deprecated" in favor of "data-root". This flag was added
 	// before Docker 1.0, so won't be removed, only hidden, to discourage its usage.
-	flags.MarkHidden("graph")
+	_ = flags.MarkHidden("graph")
 
 	flags.StringVar(&conf.Root, "data-root", defaultDataRoot, "Root directory of persistent Docker state")
 
 	flags.BoolVarP(&conf.AutoRestart, "restart", "r", true, "--restart on the daemon has been deprecated in favor of --restart policies on docker run")
-	flags.MarkDeprecated("restart", "Please use a restart policy on docker run")
+	_ = flags.MarkDeprecated("restart", "Please use a restart policy on docker run")
 
 	// Windows doesn't support setting the storage driver - there is no choice as to which ones to use.
 	if runtime.GOOS != "windows" {
@@ -75,7 +75,7 @@ func installCommonConfigFlags(conf *config.Config, flags *pflag.FlagSet) error {
 	flags.IntVar(&maxConcurrentUploads, "max-concurrent-uploads", config.DefaultMaxConcurrentUploads, "Set the max concurrent uploads for each push")
 	flags.IntVar(&conf.ShutdownTimeout, "shutdown-timeout", defaultShutdownTimeout, "Set the default shutdown timeout")
 	flags.IntVar(&conf.NetworkDiagnosticPort, "network-diagnostic-port", 0, "TCP port number of the network diagnostic server")
-	flags.MarkHidden("network-diagnostic-port")
+	_ = flags.MarkHidden("network-diagnostic-port")
 
 	flags.StringVar(&conf.SwarmDefaultAdvertiseAddr, "swarm-default-advertise-addr", "", "Set default address or interface for swarm advertised address")
 	flags.BoolVar(&conf.Experimental, "experimental", false, "Enable experimental features")

cmd/dockerd/service_windows.go

@@ -52,7 +52,7 @@ func installServiceFlags(flags *pflag.FlagSet) {
 	flRegisterService = flags.Bool("register-service", false, "Register the service and exit")
 	flUnregisterService = flags.Bool("unregister-service", false, "Unregister the service and exit")
 	flRunService = flags.Bool("run-service", false, "")
-	flags.MarkHidden("run-service")
+	_ = flags.MarkHidden("run-service")
 }
 
 type handler struct {