Deprecate the multicastInterfaces option (#3898)

Some distros have exposed the multicastInterfaces option and made it
uncommented in the config file. antrea-agent would crash if a cluster
upgrades to v1.7.0 but doesn't remove the option. This patch adds the
option back and deprecates it in a compatible manner.

Signed-off-by: Quan Tian <qtian@vmware.com>

cmd/antrea-agent/options.go

@@ -398,6 +398,10 @@ func (o *Options) validateMulticastConfig() error {
 				return err
 			}
 		}
+		if len(o.config.Multicast.MulticastInterfaces) == 0 && len(o.config.MulticastInterfaces) > 0 {
+			klog.InfoS("The multicastInterfaces option is deprecated, please use multicast.multicastInterfaces instead")
+			o.config.Multicast.MulticastInterfaces = o.config.MulticastInterfaces
+		}
 	}
 	return nil
 }

pkg/config/agent/config.go

@@ -187,6 +187,10 @@ type AgentConfig struct {
 	// 2. TransportInterfaceCIDRs
 	// 3. The Node IP
 	TransportInterfaceCIDRs []string `yaml:"transportInterfaceCIDRs,omitempty"`
+	// The names of the interfaces on Nodes that are used to forward multicast traffic.
+	// Defaults to transport interface if not set.
+	// Deprecated: use Multicast.MulticastInterfaces instead.
+	MulticastInterfaces []string `yaml:"multicastInterfaces,omitempty"`
 	// Multicast configuration options.
 	Multicast MulticastConfig `yaml:"multicast,omitempty"`
 	// AntreaProxy contains AntreaProxy related configuration options.