After aligning the blocks returned by kmalloc, we need to save the original
pointer so they can be correctly freed.

There are no guarantees about the alignment of SKB data, so we need to
handle worst case alignment.

Since right shifts over subtraction have no distributive property, we need
to fix the back pointer calculation.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/884/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>