mac80211: Send deauth/disassoc prior to dropping STA entry

When management frame protection (IEEE 802.11w) is used, the
deauthentication and disassociation frames must be protected whenever
the encryption keys are configured. We were removing the STA entry and
with it, the keys, just before actually sending out these frames which
meant that the frames went out unprotected. The AP will drop them in
such a case. Fix this by reordering the operations a bit so that
sta_info_destroy_addr() gets called only after
ieee80211_send_deauth_disassoc().

Signed-off-by: Jouni Malinen <j@w1.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>