From: Juergen Quade <quade@hsnr.de>

Lots of places in the kernel are using [v]snprintf wrongly: they assume it
returns the number of characters copied.  It doesn't.  It returns the
number of characters which _would_ have been copied had the buffer not been
filled up.

So create new functions vscnprintf() and scnprintf() which have the
expected (sane) semaptics, and migrate callers over to using them.