mwifiex: update cfg80211 with correct reason code when connection is lost

Driver gets LINK_LOST, DEAUTHENTICATED and DISASSOCIATED events
from firmware when connection is lost in different scenarios.
Currently we are using common code WLAN_REASON_DEAUTH_LEAVING
for these cases.

This patch adds support to parse an actual reason code from
firmware event body and send it to cfg80211.
WLAN_REASON_DEAUTH_LEAVING code is used if deauth is initiated
by our device.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>