rt2x00: allow AP and mesh mode to operate simultaneously

Allow AP and Mesh mode to operate concurrently using
single radio. Verify this using fonera 2.0n featuring
RT3052 chipset and also TP-LINK TL-WN727N featuring
RT5370 chipset.

Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@gmail.com>
Acked-by: Helmut Schaa <helmut.schaa@googlemal.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>