if_start() is being used here as a way of kick-starting the new queue

processing.  For if_transmit() style hardware drivers (which none publicly
exist yet, for wireless) they will need to still implement if_start()
but only to re-start the TX queue.

sys/net80211/ieee80211_proto.c

@@ -1787,6 +1787,11 @@ ieee80211_newstate_cb(void *xvap, int npending)
 		IF_LOCK(&vap->iv_ifp->if_snd);
 		vap->iv_ifp->if_drv_flags &= ~IFF_DRV_OACTIVE;
 		IF_UNLOCK(&vap->iv_ifp->if_snd);
+
+		/*
+		 * XXX Kick-start a VAP queue - this should be a method,
+		 * not if_start()!
+		 */
 		if_start(vap->iv_ifp);
 
 		/* bring up any vaps waiting on us */