DFS offload: Add main DFS handler for offloaded case

DFS offload: Add main DFS handler for offloaded case

Add handling logic for DFS offloaded case, and add a helper function
that takes the frequency (MHz) as a param and returns 1 if given channel
requires DFS, or 0 otherwise.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>