CVE-2026-19938 Use-after-free of an ATT PDU buffer when signing an outgoing Bluetooth ATT Signed Write Command fails

The Bluetooth host's ATT transmit path releases a buffer it does not own when signing fails. chansend in subsys/bluetooth/host/att.c documents and every other error exit implements the contract that on failure the caller retains ownership of the netbuf; the BTATTOPSIGNEDWRITECMD branch instead...