Enable sharing of scan result events among virtual interfaces

Enable sharing of scan result events among virtual interfaces

When controlling multiple virtual interfaces on the same physical
radio, share the scan results events with sibling interfaces. This
decreases the time it takes to connect many virtual interfaces.

This is currently only supported on Linux with cfg80211-based
drivers when using nl80211 or wext driver interface.

Signed-off-by: Ben Greear <greearb@candelatech.com>