This patch provides the utility functions to needed to synchronize the
changes made to a guest domain network device's multicast filter
with the corresponding macvtap device's filter on the host:

* Get/add/remove multicast MAC addresses
* Get the macvtap device's RX filter list
Signed-off-by: NTony Krowiak <akrowiak@linux.vnet.ibm.com>
Signed-off-by: NLaine Stump <laine@laine.org>