vmm: add VM_DESTROY ioctl call

[gusev.vitaliy_gmail.com]

Summary

If bhyve compiled with capsicum support, vm_destroy() fails because sysctl calls are not allowed.

This is counterpart of https://reviews.freebsd.org/D31325 can probably can be used as replacement.

[jhb]

Mm, this conflicts with a change I have to make destroy synchronous due to a race with destroy not finishing before bhyve restarts in a loop. I think instead you might want some sort of model where you can set a flag when creating a VM (or perhaps via an ioctl) that causes the VM to be destroyed on last close.

The conflicting change I haven't yet uploaded for review but you can see it here: https://github.com/bsdjhb/freebsd/commit/213d5795a8a1e1835bf936d1c820ffd272e68b11

[gusev.vitaliy_gmail.com]

In D34954#793575, @jhb wrote:

Mm, this conflicts with a change I have to make destroy synchronous due to a race with destroy not finishing before bhyve restarts in a loop. I think instead you might want some sort of model where you can set a flag when creating a VM (or perhaps via an ioctl) that causes the VM to be destroyed on last close.

The conflicting change I haven't yet uploaded for review but you can see it here: https://github.com/bsdjhb/freebsd/commit/213d5795a8a1e1835bf936d1c820ffd272e68b11

I will check it out and update review. Thanks.