cfg80211: enforce lack of interface combinations

My grand plan to allow drivers to gradually move over
to advertising virtual interface combinations and only
enforce with drivers that do want it enforced doesn't
seem to be working out, only Christian ever added the
advertising (to carl9170), nobody else did.

Begin enforcing combinations in cfg80211 so that users
can rely on the information reported about a device.

Cc: "Luis R. Rodriguez" <mcgrof@qca.qualcomm.com>
Cc: Jouni Malinen <jouni@qca.qualcomm.com>
Cc: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Cc: Senthil Balasubramanian <senthilb@qca.qualcomm.com>
Cc: Kalle Valo <kvalo@qca.qualcomm.com>
Cc: Jiri Slaby <jirislaby@gmail.com>
Cc: Nick Kossifidis <mickflemm@gmail.com>
Cc: Bob Copeland <me@bobcopeland.com>
Cc: Bing Zhao <bzhao@marvell.com>
Cc: Lennert Buytenhek <buytenh@wantstofly.org>
Cc: Ivo van Doorn <IvDoorn@gmail.com>
Cc: Gertjan van Wingerde <gwingerde@gmail.com>
Cc: Helmut Schaa <helmut.schaa@googlemail.com>
Cc: Luciano Coelho <coelho@ti.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>