Make use of NetUtils.getBroadcastMacAddr()

    ISSUE: I suggested to make NetUtils.broadcastMacAddr public, but that was no
           a good idea as we already have the getter and because that is an arra
           therefore vulnerable to modifications.

Change-Id: I098ca828d79ffe1d478c761d8b749ee100dfba5b
Signed-off-by: Alessandro Boch <aboch@cisco.com>