aesni(4): Avoid panicking when kmalloc() returns an unaligned pointer.

aesni(4): Avoid panicking when kmalloc() returns an unaligned pointer.

Instead, align it ourselves and keep the original address for kfree().
This is a bit hacky but not too hacky (and it is done the same way in
padlock(4)).

In the middle run, we probably need some kmalloc() flavor that can do
alignment.

In-discussion-with: alexh