Migrate nl80211 driver to key_flag API and add additional sanity checks.
I'm still not sure why we install unicast WEP keys also as default
unicast keys. Based on how I understand how mac80211 handles that it
should be pointless. I just stuck to how we do things prior to the patch
for WEP keys to not break anything. After all other drivers may need it.
Signed-off-by: Alexander Wetzel <alexander@wetzel-home.de>