ice: fix kernel BUG if register_netdev fails

If register_netdev() fails, the driver will attempt to cleanup the
q_vectors and inadvertently trigger a kernel BUG due to a NULL pointer
dereference.

This occurs because cleaning up q_vectors attempts to call
netif_napi_del on napi_structs which were never initialized.

Resolve this by releasing the netdev in ice_cfg_netdev and setting
vsi->netdev to NULL. This ensures that after ice_cfg_netdev fails the
state is rewound to match as if ice_cfg_netdev was never called.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>