[$] Checked-size array parameters in C

There are many possible programmer mistakes that are not caught by theminimal checks specified by the C language; among those is passing an arrayof the wrong size to a function. A recent attempt to add some safetyaround array parameters within the crypto layer involved the use of someclever tricks, but it turns out that clever tricks are unnecessary in thiscase. There is an obscure C feature that can cause this checking tohappen, and it is already in use in a few places within the kernel.