tests: match tcpdump RSTs to the data connection port pair

[GrahamCampbell]

I noticed this issue while working on #22304. The vsftpd RST checks matched any captured RST involving one port number on either side, but tcpdump sees all of loopback while other pytest workers run — so an unrelated RST on a recycled ephemeral port can fail them (example). The trace line already names both endpoints, so return the pair from get_data_ports() and have get_rsts() match only RSTs between exactly those two ports.

[GrahamCampbell]

PR rebased. No changes made. Ready for review. :)

[Copilot]

Pull request overview

This PR tightens the tcpdump-based FTPS/FTP shutdown tests to avoid flakiness from unrelated loopback TCP RSTs by matching RST packets only when they occur between the exact two endpoints (server/client port pair) of the FTP data connection.

Changes:

• Update VsFTPD.get_data_ports() to return (remote_port, local_port) pairs parsed from curl’s “Established 2nd connection … from … port …” trace line.
• Extend RunTcpDump.get_rsts() to support filtering by exact port pairs (port_pairs) in addition to the existing “either side matches” ports filtering.
• Update vsftpd-related shutdown tests to pass port_pairs instead of ports.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/http/testenv/vsftpd.py	Parse and return data-connection port pairs from curl trace lines.
tests/http/testenv/curl.py	Add port_pairs filtering to tcpdump RST matching logic.
tests/http/test_30_vsftpd.py	Use port_pairs for data-connection-specific RST assertions.
tests/http/test_31_vsftpds.py	Use port_pairs for data-connection-specific RST assertions.
tests/http/test_32_ftps_vsftpd.py	Use port_pairs for data-connection-specific RST assertions.

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[jay]

Thanks