mptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction

These records connect through source-stated identifiers. Shared identifiers or dates alone do not establish shared exposure, root cause or applicability.

CVE-2026-89554 · Microsoft / collected KEV context

cve-program · CVE-2026-89554

• https://git.kernel.org/stable/c/4534e0eead692bb069ad1e6a5a245fc2e2078300
• https://git.kernel.org/stable/c/63cacb05e51a1c6e1349d2e593d00fd6ef43def4
• https://git.kernel.org/stable/c/954b5ea836eb118d188975ced803448537ab8479
• https://git.kernel.org/stable/c/9df36a4846375a9b75bf42d77bfed216b0f366f9
• https://git.kernel.org/stable/c/64f2c5dd49b956a542c8c02b8dad5d262a462bba
• https://git.kernel.org/stable/c/51887ccd88791ddaa8755a7c614fda031ecf7982
• https://git.kernel.org/stable/c/bf19d166337c6488b39cb03eeeffb30a941d6326
• https://git.kernel.org/stable/c/b878dfdd12d7a5b8722a78d35e313506140ca3d9

No related operational record is retained in the current change model.