Driver switches vif sta_state into QTNF_STA_CONNECTING when cfg80211
core initiates connect procedure. Further this state is changed either
to QTNF_STA_CONNECTED or to QTNF_STA_DISCONNECTED by BSS_JOIN and
BSS_LEAVE events from firmware. However it is possible that no such
events will be sent by firmware, e.g. if EAPOL timed out.

In this case vif sta_mode will remain in QTNF_STA_CONNECTING state and
all subsequent connection attempts will fail with -EBUSY error code.
Fix this by perfroming STA state transition from QTNF_STA_CONNECTING
to QTNF_STA_DISCONNECTED in cfg80211 disconnect callback.
No need to rely upon firmware events in this case.
Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>