DESC
remap_file_pages protection support: fix try_to_unmap_one for VM_NONUNIFORM vma's
EDESC
From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

When unmapping linear but non uniform VMA's in try_to_unmap_one, we must
encode the prots in the PTE.

However, we shouldn't use the generic set_nonlinear_pte() function as it
allows for nonlinear offsets, on which we should instead BUG() in this code
path.

Additionally, add a missing TLB flush in both locations. However, there'is
some excess of flushes in these functions.
