[core] perf: size write buffers for reuse

size write buffers for reuse in common cases
(so that write buffers are BUFFER_MAX_REUSE_SIZE)

src/chunk.c

@@ -328,7 +328,7 @@ void chunkqueue_get_memory(chunkqueue *cq, char **mem, size_t *len, size_t min_s
 
 	/* default values: */
 	if (0 == min_size) min_size = 1024;
-	if (0 == alloc_size) alloc_size = 4096;
+	if (0 == alloc_size) alloc_size = 4095;
 	if (alloc_size < min_size) alloc_size = min_size;
 
 	if (NULL != cq->last && MEM_CHUNK == cq->last->type) {

src/connections.c

@@ -971,8 +971,8 @@ static int connection_read_cq(server *srv, connection *con, chunkqueue *cq, off_
 	 * if FIONREAD doesn't signal a big chunk we fill the previous buffer
 	 *  if it has >= 1kb free
 	 */
-	if (0 != fdevent_ioctl_fionread(con->fd, S_IFSOCK, &toread) || toread <= 4096) {
-		toread = 4096;
+	if (0 != fdevent_ioctl_fionread(con->fd, S_IFSOCK, &toread) || toread < 4096) {
+		toread = 4095;
 	}
 	else if (toread > MAX_READ_LIMIT) {
 		toread = MAX_READ_LIMIT;