xtables-addons: pass correct flags to compile and install
The Makefile currently redefine the Compile and Install functions.
This is not working when using an external toolchain because some
flags are not interpreted, like CROSS_COMPILE. It is possible to
override the MAKE_FLAGS and MAKE_INSTALL_FLAGS instead.
Signed-off-by: Sébastien Blin <sebastien.blin@savoirfairelinux.com>