Add fakey 'deflateBound()' function to the in-kernel zlib routines

It's not the real deflateBound() in newer zlib libraries, partly because
the upcoming usage of it won't have the "stream" available, so we can't
have the same interfaces anyway.

This uses the new deflateBound() thing to sanity-check the input to the
zlib decompressor before we even bother to start reading in the blocks.

Problem noted by Tim Yamin <plasmaroo@gentoo.org>
Signed-off-by: Chris Wright <chrisw@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>