Channel Switch will later require to generate beacons without setting
them immediately. Therefore split the presp generation in an own
function. Splitting the original very long function might be a good idea
anyway.
Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de> Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de> Signed-off-by: Johannes Berg <johannes.berg@intel.com>