iwlagn: fix dual-mode RXON

 The PAN context has three states: disabled, disassociated
 and associated. It seems that wasn't quite as much of an
 issue in previous versions of the microcode, but now we
 really have to use all the three states properly. So add
 code to switch accordingly.

Additionally, PAN parameters need to be sent differently
and the timing for PAN RXON needs to be inbetween.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>