qeth: improve ip_list administration after deregister failures

1. ip_list handling after deregister failure of multicast address:
   If error code "MC Address not found" is returned do not re-add
   multicast address to ip_list.
   For other error codes readd multicast address at the end of
   function qeth_delete_all_mc.
2. ip_list handling after deregister failure or normal ip address:
   If error code "IP Address not found" is returned do not re-add
   multicast address to ip list.
   This is especially important in IP address takeover scenarios,
   to enable re-takeover of a taken over IP address.

Signed-off-by: Ursula Braun <braunu@de.ibm.com>
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>