libnetwork: support `mode` option for bridge

L2 will be used to allow using existing bridges which netavark will
neither create nor delete.

Signed-off-by: Michael Zimmermann <sigmaepsilon92@gmail.com>

common/libnetwork/netavark/config.go

@@ -207,6 +207,10 @@ func (n *netavarkNetwork) networkCreate(newNetwork *types.Network, defaultNet bo
 				if len(value) == 0 {
 					return nil, errors.New("invalid vrf name")
 				}
+			case types.ModeOption:
+				if !slices.Contains(types.ValidBridgeModes, value) {
+					return nil, fmt.Errorf("unknown bridge mode %q", value)
+				}
 			default:
 				return nil, fmt.Errorf("unsupported bridge network option %s", key)
 			}

common/libnetwork/types/const.go

@@ -24,6 +24,9 @@ const (
 	// DefaultSubnet is the subnet that will be used for the default CNI network.
 	DefaultSubnet = "10.88.0.0/16"
 
+	BridgeModeManaged   = "managed"
+	BridgeModeUnmanaged = "unmanaged"
+
 	// valid macvlan driver mode values
 	MacVLANModeBridge   = "bridge"
 	MacVLANModePrivate  = "private"
@@ -53,6 +56,9 @@ const (
 	Netavark NetworkBackend = "netavark"
 )
 
+// ValidBridgeModes is the list of valid mode options for the bridge driver
+var ValidBridgeModes = []string{BridgeModeManaged, BridgeModeUnmanaged}
+
 // ValidMacVLANModes is the list of valid mode options for the macvlan driver
 var ValidMacVLANModes = []string{MacVLANModeBridge, MacVLANModePrivate, MacVLANModeVepa, MacVLANModePassthru}