wlcore: don't handle unsetting of default wep key

mac80211 unsets the default wep key on disassoc.
The fw doesn't support this notification, so simply
ignore it.

The actual flow actually triggers fw recovery in some
cases, as mac80211 unsets the default key only after
disassoc, when wlvif->sta.hlid, resulting in invalid
hlid being passed to the fw.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>