I have no idea why this is needed to fix kernel-headers extraction.
When testing, linux-$(LINUX_HEADERS_VERSION)/*/*/Config.in returned
a superset of linux-$(LINUX_HEADERS_VERSION)/drivers/*/Config.in
(as expected). But run by make it seems to be broken, as some driver
Config.in were missing (e.g. drivers/pci/Config.in, drivers/mtd/Config.in).