nvmet: fix heap out-of-bounds read in nvmet_auth_negotiate()

In the Linux kernel, the following vulnerability has been resolved: nvmet: fix heap out-of-bounds read in nvmet_auth_negotiate() nvmet_execute_auth_send() allocates the DH-HMAC-CHAP message buffer with the host-supplied transfer length (tl) and hands it to nvmet_auth_negotiate() without passing tl along. nvmet_auth_negotiate() then reads the negotiate header and, for each of the halen hash identifiers and dhlen DH group identifiers, indexes into the fixed idlist[60] array (hashes at idlist[0..halen), groups at idlist[30..]). Neither the transfer length nor halen/dhlen is validated. A malicious or non-conformant host can report a tl smaller than the negotiate structure, or a halen/dhlen larger than the array (both are u8, up to 255), making the loops read past the end of the allocated buffer (heap out-of-bounds read). The sibling nvmet_auth_reply() already validates tl against the structure size; the negotiate path did not. Pass tl into nvmet_auth_negotiate(), reject a tl that does not cover the negotiate data plus one full protocol descriptor, and reject halen/dhlen larger than NVME_AUTH_DHCHAP_MAX_DH_IDS.