mac80211: mark rt2x00 library packages as hidden, there's no point in allowing users to enable them without the packages that depend on them

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38684 3c298f89-4303-0410-b956-a3cf2f4a3e73