audio/virtual_oss: Add sndstat(4) support

[khng]

Summary

Fix "FATAL: Makefile: [37]: use a tab (not space) after a variable name"
as well.

[• hselasky]

Looks good!

[philip]

Approved by: philip (mentor)

But just wondering: how does this software behave when it is built on a system where sndstat.h is available but subsequently run on a system where it is not? i.e. what happens if we build a binary package on a new package builder and install the package on an older (but still supported) version of FreeBSD?

[khng]

In D29413#658895, @philip wrote:

Approved by: philip (mentor)

But just wondering: how does this software behave when it is built on a system where sndstat.h is available but subsequently run on a system where it is not? i.e. what happens if we build a binary package on a new package builder and install the package on an older (but still supported) version of FreeBSD?

The following line shall fail:
https://github.com/hselasky/virtual_oss/blob/main/virtual_main.c#L1811

The consequence of this ioctl call failing is that no virtual_oss devices will be listed in /dev/sndstat, despite the node created by virtual_oss is still presented. For the later question, our current builder will run with the lowest supported release version, so that should not happen in practise.