wil6210: wait for disconnect completion

cfg80211_ops.disconnect() should wait for disconnect flow to
complete. If it does not, internal state becomes out of sync with
one in cfg80211. If one does stress test connect/disconnect
sequence, cfg80211 will issue next connect before disconnect
completed internally.

Change-Id: I66a6a23239710c85b9cdb5824c205692c4b53866
Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: Maya Erez <qca_merez@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
Git-commit: 78771d76f826202012201d700028a2d866d03fb3
Git-repo: https://github.com/kvalo/ath.git


CRs-Fixed: 982882
Signed-off-by: Maya Erez <merez@codeaurora.org>