MINOR: contrib: add support for heartbeat control messages.

Nothing really complicated: add a new control message type for such heartbeat
messages.
diff --git a/contrib/wireshark-dissectors/peers/packet-happp.c b/contrib/wireshark-dissectors/peers/packet-happp.c
index a5e2564..32c0ec2 100644
--- a/contrib/wireshark-dissectors/peers/packet-happp.c
+++ b/contrib/wireshark-dissectors/peers/packet-happp.c
@@ -147,6 +147,7 @@
 	PEER_MSG_CTRL_RESYNCFINISHED,
 	PEER_MSG_CTRL_RESYNCPARTIAL,
 	PEER_MSG_CTRL_RESYNCCONFIRM,
+	PEER_MSG_CTRL_HEARTBEAT,
 };
 
 /* Error messages */
@@ -533,6 +534,8 @@
 		return "resync. partial";
 	case PEER_MSG_CTRL_RESYNCCONFIRM:
 		return "resync. confirm";
+	case PEER_MSG_CTRL_HEARTBEAT:
+		return "heartbeat";
 	default:
 		return "Unknown";
 	}