When DFS_RANDOM_CH_FLAG_NO_DFS_CH set, the random channel
selection will pick non-dfs channel. But currently the
MCL API utils_dfs_get_channel_list doesn't populate
the DFS flags "WLAN_CHAN_DFS" for dfs channel.
That causes the dfs_prepare_random_channel_for_freq API
can't identify DFS channel.
Fix by set WLAN_CHAN_DFS for dfs channel
Change-Id: I7ead760ddc77c198a630d12960e775961840796c
CRs-Fixed: 3016746