iov_iter: move into its own file (bug fix)

I found the problem. iov_iter_shorten() wasn't setting i->count to the new
value.

This fixes it. I'll fix the patchset tomorrow.

Thanks,
Shaggy
Merge branch 'uber-jb43' of https://github.com/Cl3Kener/HERC-KERNELS into uber-jb43