usteer: add option for probe steering

usteer: add option for probe steering

Probe suppression is mostly useful in high density deployments, where
all APs responding to all client probes would result in all channels
being saturated. It effectively hides APs from clients, and can cause
problems in normal density deployments.

Add an option for it, so it can be disabled.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>
Acked-by: David Bauer <mail@david-bauer.net>