Convert unuse_process pagetable walkers to loops using p?d_addr_end; but
correct its name to unuse_mm, rename its levels to _range as elsewhere.

Leave unuse_pte out-of-line since it's so rarely called; but move the
funny activate_page inside it.  foundaddr was a leftover from before: we
still want to break out once page is found, but no need to pass addr up.
And we need not comment on the page_table_lock at every level.

Whereas most objects shrink ~200 bytes text, swapfile.o grows slightly:
it had earlier been converted to the addr,end style to fix a 4level bug.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>