Bluetooth: L2CAP: Fix null-ptr-deref in l2cap_sock_get_sndtimeo_cb()

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SUSE CVE-2026-45836

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: L2CAP: Fix null-ptr-deref in l2capsockgetsndtimeocb Add the same NULL guard already present in l2capsockresumecb and l2capsockreadycb...