as maintained in https://github.com/sabotage-linux/kernel-headers .
downloading (and extracting) a 100+ MB kernel source tarball just for
the headers is extremely inefficient.
sabotage linux' kernel-headers tarball provides the same (including
musl compatibility fixes) in ~800 KB.
in order to use it, specify
LINUX_VER = headers-4.4.2-4
in your config.mak.
if LINUX_VER lacks the "headers-" prefix, the official source tarball
will be downloaded as usual.
rofl0r