[multicast] fix the issue multicast does not work if antreaPolicy is …

…disabled

Currently, packetIn reason only supports 0 and 1. There is no more available packetIn reasons
as traceflow and antreaPolicy use both. Multicast reuses packetIn reason with antreaPolicy, and
uses a different register bit to indicate the real reason. There is no queue for packetIn reason
'PacketInReasonNP' if antreaPloicy is disabled. And multicast will not work then.

This patch fixes #3808

Signed-off-by: Bin Liu <biliu@vmware.com>

cmd/antrea-agent/agent.go

@@ -638,7 +638,8 @@ func run(o *Options) error {
 	if features.DefaultFeatureGate.Enabled(features.Traceflow) {
 		packetInReasons = append(packetInReasons, uint8(openflow.PacketInReasonTF))
 	}
-	if features.DefaultFeatureGate.Enabled(features.AntreaPolicy) {
+	if features.DefaultFeatureGate.Enabled(features.AntreaPolicy) ||
+		features.DefaultFeatureGate.Enabled(features.Multicast) {
 		packetInReasons = append(packetInReasons, uint8(openflow.PacketInReasonNP))
 	}
 	if len(packetInReasons) > 0 {