nbd: don't allow reconnect after disconnect

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

CVE-2025-21731 · Microsoft / collected KEV context

cve-program · CVE-2025-21731

• https://git.kernel.org/stable/c/e70a578487a47d7cf058904141e586684d1c3381
• https://git.kernel.org/stable/c/6bef6222a3f6c7adb6396f77f25a3579d821b09a
• https://git.kernel.org/stable/c/e3be8862d73cac833e0fb7602636c19c6cb94b11
• https://git.kernel.org/stable/c/e7343fa33751cb07c1c56b666bf37cfca357130e
• https://git.kernel.org/stable/c/d208d2c52b652913b5eefc8ca434b0d6b757f68f
• https://git.kernel.org/stable/c/a8ee6ecde2b7bfb58c8a3afe8a9d2b848f580739
• https://git.kernel.org/stable/c/9793bd5ae4bdbdb2dde401a3cab94a6bfd05e302
• https://git.kernel.org/stable/c/844b8cdc681612ff24df62cdefddeab5772fadf1

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