ath9k: use ap style beaconing for mesh

Chun-Yeow and Javier Lopez contributed these changes to
make mesh mode use the more similar AP beaconing mode and
queue parameters. Should improve PS performance, interface
concurrency (AP modes can coexist), and beacon interval
stability.

AR9271 (ath9k_htc) mesh interfaces also need to be in AP
operating mode.

Signed-off-by: Thomas Pedersen <thomas@cozybit.com>