ksmbd: fix out-of-bound read in smb2_write

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix out-of-bound read in smb2_write ksmbd_smb2_check_message doesn't validate hdr->NextCommand. If ->NextCommand is bigger than Offset + Length of smb2 write, It will allow oversized smb2 write length. It will cause OOB read in smb2_write.