cnic: Simplify netdev events handling.

After this earlier commit to simplify probing:

    commit 4bd9b0ff
    cnic, bnx2x, bnx2: Simplify cnic probing.

we can now reliably receive netdev events and we can simplify the handling
of these events.  We now remove the logic that tries to handle missed
NETDEV_REGISTER events.

This change will allow cleanup to be simplified in the next patch.  We can
now rely on the play back of netdev events during
unregister_netdevice_notifier() to cleanup the structures.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>