mwifiex: clear previous security setting during association

Driver maintains different flags for WEP, WPA, WPA2 security modes.
Appropriate flag is set using security information provided in
connect request. mwifiex_is_network_compatible() routine uses them
to check if driver's setting is compatible with AP. Association is
aborted if the routine fails.

For some corner cases, it is observed that association is failed
even for valid security information based on association history.
This patch fixes the problem by clearing previous security setting
during each association.

We should set WEP key provided in connect request as default tx key.
This missing change is also added here.

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>