band-steering: add band-steering component

This adds a new band-steering component to usteer.

With band-steering enabled, usteer will attempt to move clients with a
consistently good SNR / signal from 2.4 GHz to the 5 GHz band.

In contrast to existing policies usteer tracks, band-steering is
non-invasive and will not lead to forceful connection termination.

Signed-off-by: David Bauer <mail@david-bauer.net>

main.c

@@ -99,6 +99,9 @@ void usteer_init_defaults(void)
 
 	config.steer_reject_timeout = 60000;
 
+	config.band_steering_interval = 120000;
+	config.band_steering_min_snr = -60;
+
 	config.roam_kick_delay = 10000;
 	config.roam_process_timeout = 5 * 1000;
 	config.roam_scan_tries = 3;