Fix dut_port_config list/dict inconsistency in traffic_generation.py

[MahekPatel-2403]

Description of PR

Fixes the inconsistency in multi_base_traffic_config() where
dut_port_config was initialized as a list but later accessed as a
dictionary using "Tx" and "Rx" keys.

Changes:

• Update dut_port_config initialization to use a dictionary
• Update TX/RX peer port insertion logic
• Update function documentation to reflect the correct structure

Summary:
Fixes #22197

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation update

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: MahekPatel-2403 / name: Mahek Patel (5e39ff4)

[mssonicbld]

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[mssonicbld]

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[mssonicbld]

Hi, there are workflow run(s) waiting for approval, you may be first-time contributor. I will notify maintainers to help approve once PR is approved. Thanks!

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