Reordered Makefile according to
https://github.com/openwrt/packages/pull/9399#issuecomment-508727872 .
Added PKG_BUILD_PARALLEL for faster compilation.
Remove duplicated conffiles section.
Install /etc/config/stubby using INSTALL_CONF, as is done elsewhere
Run init script through shellcheck and clean it up.
Added chmod for the stubby config file, to fix a LuCI issue.
Signed-off-by: Rosen Penev <rosenp@gmail.com>