ieee802154: admin-gate legacy LLSEC dump operations

Summary

In the Linux kernel, the following vulnerability has been resolved: ieee802154: admin-gate legacy LLSEC dump operations In net/ieee802154/netlink.c, the legacy IEEE802154_NL family ops table builds the LLSEC dump entries (LLSEC_LIST_KEY, LLSEC_LIST_DEV, LLSEC_LIST_DEVKEY, LLSEC_LIST_SECLEVEL) with IEEE802154_DUMP() which sets no .flags, so generic netlink runs them ungated. The modern nl802154 family admin-gates the equivalent reads via NL802154_CMD_GET_SEC_KEY and friends with .flags = GENL_ADMIN_PERM. Any local uid that can open AF_NETLINK / NETLINK_GENERIC can resolve the "802.15.4 MAC" family and dump LLSEC_LIST_KEY on any wpan netdev that has an LLSEC key installed; the dump handler writes the raw 16-byte AES-128 key bytes (IEEE802154_ATTR_LLSEC_KEY_BYTES, copied verbatim from struct ieee802154_llsec_key.key) into the reply. Recovering the AES key compromises 802.15.4 LLSEC link confidentiality and authenticity, since LLSEC uses CCM* and the same key authenticates and encrypts frames. Impact: any local uid with no capabilities can read the raw 16-byte AES-128 LLSEC key from the kernel keytable on any wpan netdev that has an administrator-installed LLSEC key, by issuing an LLSEC_LIST_KEY dump on the legacy IEEE802154_NL generic-netlink family. Introduce IEEE802154_DUMP_PRIV() mirroring IEEE802154_DUMP() but setting .flags = GENL_ADMIN_PERM, and use it for the four LLSEC dump entries. LIST_PHY and LIST_IFACE retain IEEE802154_DUMP() because the modern nl802154 family exposes their equivalents to unprivileged readers by design (NL802154_CMD_GET_WPAN_PHY and NL802154_CMD_GET_INTERFACE carry "can be retrieved by unprivileged users" annotations).