d/config: fix default-network-opts in daemon.json

Prevent the daemon from erroring out if daemon.json contains default
network options for network drivers aside from bridge. Configuring
defaults for the bridge driver previously worked by coincidence because
the unrelated CLI flag '--bridge' exists.

Signed-off-by: Cory Snider <csnider@mirantis.com>

daemon/config/config.go

@@ -76,12 +76,13 @@ var builtinRuntimes = map[string]bool{
 // Use this to differentiate these options
 // with others like the ones in TLSOptions.
 var flatOptions = map[string]bool{
-	"cluster-store-opts": true,
-	"log-opts":           true,
-	"runtimes":           true,
-	"default-ulimits":    true,
-	"features":           true,
-	"builder":            true,
+	"cluster-store-opts":   true,
+	"default-network-opts": true,
+	"log-opts":             true,
+	"runtimes":             true,
+	"default-ulimits":      true,
+	"features":             true,
+	"builder":              true,
 }
 
 // skipValidateOptions contains configuration keys

daemon/config/config_linux_test.go

@@ -25,6 +25,11 @@ func TestGetConflictFreeConfiguration(t *testing.T) {
 			},
 			"log-opts": {
 				"tag": "test_tag"
+			},
+			"default-network-opts": {
+				"overlay": {
+					"com.docker.network.driver.mtu": "1337"
+				}
 			}
 		}`)
 
@@ -33,6 +38,7 @@ func TestGetConflictFreeConfiguration(t *testing.T) {
 	flags.BoolVarP(&debug, "debug", "D", false, "")
 	flags.Var(opts.NewNamedUlimitOpt("default-ulimits", nil), "default-ulimit", "")
 	flags.Var(opts.NewNamedMapOpts("log-opts", nil, nil), "log-opt", "")
+	flags.Var(opts.NewNamedMapMapOpts("default-network-opts", nil, nil), "default-network-opt", "")
 
 	cc, err := getConflictFreeConfiguration(configFile, flags)
 	assert.NilError(t, err)