nl80211: fix corrupt scan results from wpa_supplicant

[wryun]

Without clearing the scanlist entries, it was possible to have bad data remaining from previous calls in the ht_operation/vht_operation fields (not set here). This could cause segfaults in rpcd's iwinfo module, as it was possible that (a) the primary_chan would not be 0 and therefore (b) you would use bad data for chan_width etc. as an index into short-ish array:

if (e->ht_chan_info.primary_chan) {
	t = blobmsg_open_table(&buf, "ht_operation");
	blobmsg_add_u32(&buf, "primary_channel", e->ht_chan_info.primary_chan);
	blobmsg_add_string(&buf, "secondary_channel_offset", ht_secondary_offset[e->ht_chan_info.secondary_chan_off]);
	blobmsg_add_u32(&buf, "channel_width", ht_chan_width[e->ht_chan_info.chan_width]);
	blobmsg_close_table(&buf, t);
}

[Neustradamus]

@wryun: Nice PR :)