fix(fcc): support huawei short response with double sockets

[stackia]

Summary

This PR adds Huawei-specific FCC double socket support and handles Huawei short FCC responses that do not include NAT traversal fields.

What changed

• Add a separate FCC media socket for Huawei while keeping Telecom/ZTE/Fiberhome on the existing single socket path.
• Bind Huawei FCC sockets as an adjacent pair: media port N, signaling port N + 1.
• Support Huawei FMT=6/type=2 short responses with 24 bytes by parsing first_seq and bitrate, then waiting for unicast instead of falling back to multicast.
• Keep full Huawei response NAT traversal behavior, sending NAT packets from the media socket when available.
• Preserve the existing receive classification path: RTCP packets go to FCC response handling, non-RTCP packets go to unicast media handling.
• Ignore duplicate redirect responses for both Telecom and Huawei without consuming redirect budget.
• Expand FCC e2e coverage for Huawei short responses, redirect-to-short responses, Telecom redirect duplicates, and single-socket media behavior when the signal port changes.

Validation

• git diff --check
• cmake --build build -j$(getconf _NPROCESSORS_ONLN) | tail -100
• ./scripts/run-e2e.sh test_fcc.py -p 1 | tail -120

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[Copilot]

Pull request overview

This PR extends the FCC (Fast Channel Change) implementation to better support Huawei-specific behaviors by introducing a dedicated Huawei media socket (paired with the signaling socket) and by correctly handling Huawei “short” (24-byte) FCC responses that omit NAT traversal fields.

Changes:

• Add Huawei-only dual-socket support (adjacent media/signaling UDP ports) while keeping other FCC types on the single-socket path.
• Update FCC event handling to drain/process packets from either the signaling or media socket.
• Expand E2E coverage for Huawei short responses and redirect flows, and for Telecom redirect duplicates / signal-port changes.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/stream.c	Routes events for both FCC signaling socket and (new) Huawei media socket into FCC handling.
src/fcc.h	Extends FCC session state with Huawei media socket/client address fields and updates handler signature.
src/fcc.c	Implements dual-socket creation/binding/registration and refactors bind logic into reusable helpers.
src/fcc_telecom.c	Ignores duplicate redirect responses without consuming redirect budget.
src/fcc_huawei.c	Supports Huawei short (24-byte) responses, improves response logging, and ignores duplicate redirects.
e2e/test_fcc.py	Adds E2E tests covering Huawei short responses, redirect→short, and Telecom redirect duplicate handling.
e2e/helpers/mock_fcc.py	Enhances MockFCCServer to emit short Huawei responses, redirect responses, and adjusted Huawei unicast send port behavior.

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