Updated the example of FatTree with TCP.

[cying17]

This PR updates the example of FatTree with TCP to make the setting more realistic.

Description

Changed the example to use 1024 bytes per packet, arrival_dist of 0.0008 (10Mbps), port rate of 10000000000 (10Gbps).

How has this been tested?

python examples/fattree_tcp.py

Types of changes

• Bug fix (non-breaking change which fixes an issue) Fixes #
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.