wl12xx: check the actual vif operstate in wl1271_dev_notify

The current wl1271_dev_notify implementation sets the
new operstate to all associated stations (while only
a specific vif was changed).

Until we'll have a method to get the actual vif from
the given dev, check the current operstate of each vif.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>