mac80211: fix ieee80211_set_disassoc() sending DelBA

When ieee80211_set_disassoc() is called with the
tx argument set to true, it will send DelBA out
to the peer. This isn't useful or necessary in a
few cases where we do it today, those being when
we lost the connection or when the supplicant
explicitly asked us to not tell the AP.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>