Include secondary protocol flag always

This way if you have the value set in config (even as "") it'll get
passed down to allow you to override the default config

Fixes #9006

nodeup/pkg/model/protokube.go

@@ -361,7 +361,7 @@ type ProtokubeFlags struct {
 	GossipListen   *string `json:"gossip-listen" flag:"gossip-listen"`
 	GossipSecret   *string `json:"gossip-secret" flag:"gossip-secret"`
 
-	GossipProtocolSecondary *string `json:"gossip-protocol-secondary" flag:"gossip-protocol-secondary"`
+	GossipProtocolSecondary *string `json:"gossip-protocol-secondary" flag:"gossip-protocol-secondary" flag-include-empty:"true"`
 	GossipListenSecondary   *string `json:"gossip-listen-secondary" flag:"gossip-listen-secondary"`
 	GossipSecretSecondary   *string `json:"gossip-secret-secondary" flag:"gossip-secret-secondary"`
 }