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.

Note:
In fact, it caused fluctuating ifstatus reports for a slave interface depending on where in the bringup phase we were. Sometimes the master was correctly reported:

eth2            up
	link:     #4, state up, mtu 1500, master br2
	type:     ethernet, hwaddr 52:54:00:d1:0b:a8
	config:
	compat:/etc/sysconfig/network/ifcfg-eth2

And sometimes not:

eth2            up
	link:     #4, state up, mtu 1500
	type:     ethernet, hwaddr 52:54:00:d1:0b:a8
	config:
	compat:/etc/sysconfig/network/ifcfg-eth2