wlan - use wlan_global_serializer as if serializer

This fixes problems on SMP system using ath(4).

suggested-by: Sepherosa Ziehau <sepherosa@gmail.com>
iwn - don't acquire wlan_global_serializer in iwn_start()

With abc2d9274 iwn_start() is called with wlan_global_serializer
held already.
wlan - wlan_assert_serialized in ieee80211_init/_start/_ioctl
ath - wlan_assert_serialized in ath_init/_start/_ioctl
iwn - wlan_assert_serialized in iwn_init/_start/_ioctl
merge
merge
Merge branch 'master' of git://git.dragonflybsd.org/dragonfly into wlan_serialize
ral: release wlan serializer while loading firmware
Merge branch 'master' of git://git.dragonflybsd.org/dragonfly into wlan_serialize
Merge remote-tracking branch 'hofmann/wlan_serialize'
bnx: Pack TX mbuf and dmamap together; improve cache utilization