[dtrace] syscall provider naming convention.

[Artem Belevich]

> I have one comment though.  I am not sure about renaming syscall.ko to
> syscall_freebsd.ko.

You mean systrace_freebsd.ko.

I've renamed it for consistency with other systrace provider variants.
I can change it back.

> Perhaps we could keep the old name?  Or add a new module
> under that name that would load native syscall module and all emulation syscall
> modules (if any)?

I'm not sure that creating an umbrella 'systrace' module is worth it.
"kldload /boot/kernel/systrace*" should do that just fine. The reason
dtrace exists is that there are number of modules with dtrace
providers that are not easily distinguishable by their name.

--Artem