Update comments in cluster_legacy.h

Update comment suggesting clusterMsgPingExtTypes to clusterMsgPingtypes as clusterMsgPingExtTypes does not exist. Additionally specify that ver is set to CLUSTER_PROTO_VER, not "1", to make it easier to see where to change this.

Signed-off-by: Ben Totten <btotten@amazon.com>

src/cluster_legacy.h

@@ -208,7 +208,7 @@ union clusterMsgData {
 typedef struct {
     char sig[4];        /* Signature "RCmb" (Cluster message bus). */
     uint32_t totlen;    /* Total length of this message */
-    uint16_t ver;       /* Protocol version, currently set to 1. */
+    uint16_t ver;       /* Protocol version, currently set to CLUSTER_PROTO_VER. */
     uint16_t port;      /* Primary port number (TCP or TLS). */
     uint16_t type;      /* Message type */
     uint16_t count;     /* Only used for some kind of messages. */