When we disable SRIOV, we used to unregister the netdev but wasn't
freed. But next time when the same netdev is registered, since the state
was in 'NETREG_UNREGISTERED', we used to hit BUG_ON in register_netdevice,
where it expects the state to be 'NETREG_UNINITIALIZED'.

Alloc netdev and register them while configuring SRIOV, and free them
when SRIOV is disabled. Also added a new function to setup ethernet
properties instead of using ether_setup. Set carrier off by default,
since we don't have to do any transmit on the interface.

Fixes: 7829451c ("cxgb4: Add control net_device for configuring PCIe VF")
Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>