wl12xx: fix DFS channels handling in scheduled scan

DFS channels were never getting included in the scheduled scans,
because they always contain the passive flag as well and the call was
asking for DFS and active channels.

Fix this by ignoring the passive flag when collecting DFS channels.
Also, move the DFS channels in the channel list before the 5GHz active
channels (this was implemented in the FW differently than specified).

Signed-off-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>