Fixes build against kernel 4.14.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>

As jool builds a kernel module, a PKG_BUILD_DIR under KERNEL_BUILD_DIR must
be used to avoid reusing build artifacts when switching to a different
target of the same architecture. Otherwise, kernel ABI mismatches may
result, leading to an unusuable module, or build failures like the
following:

    Package kmod-jool is missing dependencies for the following libraries:
    crypto_hash.ko

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>

fix Makefile chmod (644)
replace MD5SUM with HASH
add PKG_MIRROR_HASH when PKG_SOURCE_PROTO:=git

(PKG_SOURCE_PROTO:=svn tarballs are not reproducible for now)

Signed-off-by: Etienne Champetier <champetier.etienne@gmail.com>

Signed-off-by: Dan Luedtke <mail@danrl.com>

Latest upstream changes explicitly include `net/ip6_checksum.h`.
Fixes issue #3657.

Signed-off-by: Dan Luedtke <mail@danrl.com>

This adds support for the Jool SIIT/NAT64 translating kernel modules and user
space tools.

Signed-off-by: Dan Luedtke <mail@danrl.com>