Fix fragmentation cache

[TheSableCZ]

Summary

Several fixes related to fragmentation cache and parser issues.

Details

• Fragmentation stats were incorrectly computed because recursion in put_pkt method.
• The subsequent fragments (not the first ones) were filled with random ports because the parser continued parsing the L4 layer.
• Packet data were not reset correctly in parser.

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✅ Checks

• Relevant documentation was updated (if needed)
• CI pipeline passes (build, tests, lint, static analysis)
• New code follows clang-tidy rules
• The change is clearly related to a specific issue / requirement
• Documentation (e.g. Doxygen) is updated if needed
• The PR is rebased on the latest master
• No unrelated changes are included

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