tch starts at 1,
just like in previous kernels, but also just like in previous kernels
it's possible for it to wrap back to 0.  This preserves the kernel
functionality exactly like it was before the patch (neither method broke
the spec)

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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