Fix averager speed for TCP connections (#373)
Experimentally, we have found that these two changes fixes the averaging speed problem for TCP connections:
1. Change `DEFAULT_PART_SIZE_BYTES` from `2 ** 19` to `2 ** 16`
2. Revert the p2pd dependencies to the state of Jun 1, 2021
Co-authored-by: justheuristic <justheuristic@gmail.com>