ZBeacon binds to wrong interface (or no option to specify broadcast interface)

[kylemallory]

When trying to broadcast beacons on a system with multiple network interfaces, broadcasts are not seen on all interfaces.
It appears that in a multi-network interface environment, ZBeacon will bind to an "automatically selected" interface (per java.nio.DatagramChannel docs). Subsequent broadcasts are only issued on that interface, potentially preventing it from broadcasting beacons on the correct network. Changing the "host" parameter in the ZBeacon constructor only changes the address to which broadcasts are broadcast to, but not the interface to which broadcasts are sent from.
ZBeacon should have a parameter that allows the user to specify the address (and thus interface) from which beacons should originate.