iwlagn: fix interface combinations

My patch to advertise interface combinations
worked by pure luck in the P2P case, but all
other cases are broken. This is due to a dumb
mistake in the code that checks what should
be advertised, fix that.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>