cfg80211: Fix BIP (AES-CMAC) cipher validation

This cipher can be used only as a group management frame cipher and as
such, there is no point in validating that it is not used with non-zero
key-index. Instead, verify that it is not used as a pairwise cipher
regardless of the key index.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
[change code to use switch statement which is easier to extend]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>