mptcp: fix NULL pointer in can_accept_new_subflow

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CVE-2025-23145 · Microsoft / collected KEV context

cve-program · CVE-2025-23145

• https://git.kernel.org/stable/c/8cf7fef1bb2ffea7792bcbf71ca00216cecc725d
• https://git.kernel.org/stable/c/b3088bd2a6790c8efff139d86d7a9d0b1305977b
• https://git.kernel.org/stable/c/855bf0aacd51fced11ea9aa0d5101ee0febaeadb
• https://git.kernel.org/stable/c/7f9ae060ed64aef8f174c5f1ea513825b1be9af1
• https://git.kernel.org/stable/c/dc81e41a307df523072186b241fa8244fecd7803
• https://git.kernel.org/stable/c/efd58a8dd9e7a709a90ee486a4247c923d27296f
• https://git.kernel.org/stable/c/4b2649b9717678aeb097893cc49f59311a1ecab0
• https://git.kernel.org/stable/c/443041deb5ef6a1289a99ed95015ec7442f141dc

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