I have a mid 2013 MacBook Air and just bought an AirPort Extreme today to replace a 2009 time capsule. The MBA does not seem to be connecting in "ac" mode. See attached screenshot showing b/g/n. Anything specific I'm supposed to do to make the fastest mode work? I assume it would show up in Airport Utility as "ac" if it were working but maybe I'm wrong. Thanks in advance.