ath5k: allow AP and mesh mode to operate simultaneously

This patch allows the possibility of having the mesh point and AP to be operated
simultaneously in one single radio. Previously, mesh point fails to generate the
mesh beacon if virtual AP is created for the same radio.

Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>