Avoid FreeBSD-SA-20:06.if_ixl_ioctl

[master-q]

• FreeBSD-SA-20:06.if_ixl_ioctl
• https://github.com/freebsd/freebsd/commit/cf3b0bdee1d2f7ec186d9eda3e19bd879887a0c0

It's also caused by unprivileged access. Such privilege may be easily avoided by ATS and VeriFast.

[master-q]

• ixl_handle_nvmupd_cmd just updates device firmware
• There are no hints that caller should call priv_check
• We can't avoid this issue