WiFi chip in SDXPRAIRIE supports DBS, and it is OK to start AP+AP in
DFS channel in DBS mode.
If CONFIG_FEATURE_WLAN_STA_AP_MODE_DFS_DISABLE is defined, AP+AP in
DFS channel in DBS mode fails to start.
Remove CONFIG_FEATURE_WLAN_STA_AP_MODE_DFS_DISABLE definition to make
AP+AP in DFS channel in DBS mode work for SDXPRAIRIE.
Change-Id: I1947b480aca2acb3245350c73935f6a4f9af964f
CRs-Fixed: 2459215