mac80211_hwsim: advertise interface combinations

Enforcing interface combinations broke uses of hwsim
with multiple virtual interfaces. Advertise that all
combinations are possible to fix this.

Reported-by: Nirav Shah <nirav.j2.shah@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>