ath9k_htc: Add support for mesh interfaces

More specifically, enable AP-style beaconing on mesh
ifaces and change the hw capabilities to reflect mesh
support.

Coexistence with a virtual STA interface was tested as
working fine.

Signed-off-by: Javier Cardona <javier@cozybit.com>
[rebase, add iface combinations]
Signed-off-by: Thomas Pedersen <thomas@cozybit.com>
ath9k_htc: Claim support for mgmt frame protection

Advertise support for management frame protection in hardware.

Signed-off-by: Javier Cardona <javier@cozybit.com>
ath9k: have mesh use ap style beaconing

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>