engine: Block multicast MAC addresses for vNICs

The patch blocks the possibility to provide a non-
unicast mac address to the vnic: neither broadcast
or multicast mac addresses aren't allowed for a vnic.

Change-Id: Ida4082be249391494053b56540d5458fecec65da
Bug-Url: https://bugzilla.redhat.com/1011912
Signed-off-by: Moti Asayag <masayag@redhat.com>