MINOR: backend: use a single call to ha_random32() for the random LB algo

For the random LB algorithm we need a random 32-bit hashing key that used
to be made of two calls to random(). Now we can simply perform a single
call to ha_random32() and get rid of the useless operations.

src/backend.c

@@ -540,8 +540,7 @@ static struct server *get_server_rnd(struct stream *s, const struct server *avoi
 	curr = NULL;
 	do {
 		prev = curr;
-		/* ensure all 32 bits are covered as long as RAND_MAX >= 65535 */
-		hash = ((uint64_t)ha_random() * ((uint64_t)RAND_MAX + 1)) ^ ha_random();
+		hash = ha_random32();
 		curr = chash_get_server_hash(px, hash, avoid);
 		if (!curr)
 			break;