IoctlSetPointerInt is necessary for interacting with the PPP kernel
driver, which wants it passed as a pointer to int, rather than the
more conventional int cast as a pointer.

We can technically do this already with
IoctlSetInt(int(uintptr(unsafe.Pointer(&foo)))), but that's just
masking the operation we're trying to execute in the first place,
and relying on the internals of IoctlSetInt to do the right
inverse transformation.

Change-Id: I1e6a1dd6190c11f06c6f5393cd2cae453939878a
GitHub-Last-Rev: a88f56073d04b02d9c076b112adaf99169a49513
GitHub-Pull-Request: golang/sys#25
Reviewed-on: https://go-review.googlesource.com/c/150321
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>