util: netlink function to delete any network device
    
    libvirt has always used the netlink RTM_DELLINK message to delete
    macvtap/macvlan devices, but it can actually be used to delete other
    types of network devices, such as bonds and bridges. This patch makes
    virNetDevMacVLanDelete() available as a generic function so it can
    intelligibly be called to delete these other types of interfaces.