Make ranges jump address space gaps

[mkroening]

I recently discovered that this range panics during iteration, even though it does not even cross the address space gap:

let pages = PageRangeInclusive {
	start: Page::<Size4KiB>::from_start_address(VirtAddr::new(0x0000_7fff_ffff_f000))
		.unwrap(),
	end: Page::<Size4KiB>::from_start_address(VirtAddr::new(0x0000_7fff_ffff_f000))
		.unwrap(),
};

We could use #616 to fix that, similar to #617. I believe it makes more sense to jump the gap, as proposed in #589 and already done via the unstable Step trait.