hostapd: merge an upstream patch for pmksa cache

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

Backport of r42762

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@42763 3c298f89-4303-0410-b956-a3cf2f4a3e73