mac80211: use the correct capability info in ieee80211_set_associated()

If an AP is beaconing with different capabilities than the one we get
in the associate response, we were still using the capabilities
received in the beacons.  One example is when the AP is beaconing with
the short slot bit set to zero and then we try to connect to it with
long slot.  In this case, we would keep using long slot until the next
beacon was received.

Fix this by using the correct capability value when calling
ieee80211_handle_bss_capability().  We were using cbss->capability,
but we should use the bss_conf->assoc_capability instead.

Signed-off-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>