Add REDIS_BIND_ADDR access macro

We need to access (bindaddr[0] || NULL) in a few places, so centralize
access with a nice macro.

src/cluster.c

@@ -2794,8 +2794,7 @@ void clusterCron(void) {
             clusterLink *link;
 
             fd = anetTcpNonBlockBindConnect(server.neterr, node->ip,
-                node->port+REDIS_CLUSTER_PORT_INCR,
-                    server.bindaddr_count ? server.bindaddr[0] : NULL);
+                node->port+REDIS_CLUSTER_PORT_INCR, REDIS_BIND_ADDR);
             if (fd == -1) {
                 redisLog(REDIS_DEBUG, "Unable to connect to "
                     "Cluster Node [%s]:%d -> %s", node->ip,

src/redis.h

@@ -367,6 +367,9 @@
 #define REDIS_NOTIFY_EVICTED (1<<9)     /* e */
 #define REDIS_NOTIFY_ALL (REDIS_NOTIFY_GENERIC | REDIS_NOTIFY_STRING | REDIS_NOTIFY_LIST | REDIS_NOTIFY_SET | REDIS_NOTIFY_HASH | REDIS_NOTIFY_ZSET | REDIS_NOTIFY_EXPIRED | REDIS_NOTIFY_EVICTED)      /* A */
 
+/* Get the first bind addr or NULL */
+#define REDIS_BIND_ADDR (server.bindaddr_count ? server.bindaddr[0] : NULL)
+
 /* Using the following macro you can run code inside serverCron() with the
  * specified period, specified in milliseconds.
  * The actual resolution depends on server.hz. */