util: functions to manage bridge fdb (forwarding database)
    
    These two functions use netlink RTM_NEWNEIGH and RTM_DELNEIGH messages
    to add and delete entries from a bridge's fdb. The bridge itself is
    not referenced in the arguments to the functions, only the name of the
    device that is attached to the bridge (since a device can only be
    attached to one bridge at a time, and must be attached for this
    function to make sense, the kernel easily infers which bridge's fdb is
    being modified by looking at the device name/index).