util: new function virNetDevOpenvswitchInterfaceGetMaster()
This function retrieves the name of the OVS bridge that the given
netdev is attached to. This separate function is necessary because OVS
set the IFLA_MASTER attribute to "ovs-system" for all netdevs that are
attached to an OVS bridge, so the standard method of retrieving the
master can't be used.
Signed-off-by: Laine Stump <laine@laine.org> ACKed-by: Michal Privoznik <mprivozn@redhat.com>