Make some network uapi headers detect if they are included after
not only glibc but also musl headers.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46161 3c298f89-4303-0410-b956-a3cf2f4a3e73