mac80211 and IEEE80211_CONF_SHORT_SLOT_TIME

Hi,

I just realised that for whatever reason mac80211 isn't setting the
IEEE80211_CONF_SHORT_SLOT_TIME flag. I'm not sure when or why that was
removed, but clearly it isn't used.

Can you please fix the drivers using it (b43, b43legacy, iwlwifi, p54,
rt2x00, rtl8180, rtl8187) to use the bss_conf's use_short_slot instead?
I'll fix mac80211 to set that appropriately.

johannes