iflist: free masterdev name if it references invalid device

We were freeing masterdev.name on a successful call to
ni_netdev_ref_bind_ifname(). This prevented ifstatus from reporting master
devices correctly for bridges/bonds.
ifstatus: slave device reporting
Merge pull request #416 from kmroz/ifla-master-fix

iflist: free masterdev name if it references invalid device
Merge pull request #417 from kmroz/ifstatus-enslave-rc1

ifstatus: slave device reporting