wlcore: allow using dfs channels

Since we are going to support dfs channels, there
is no reason to mark them as NO_IR (having
the DFS flag is enough anyway).

Additionally, when setting the regdomain configuration,
enable usable dfs channels.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>