qeth: new message if OLM limit is reached

z/OS may activate Optimized Latency Mode (OLM) for a connection
through an OSA Express3 adapter, which reduces the number of
allowed concurrent connections, if adapter is used in shared mode.
Create a meaningful message, if activation of an OSA-connection fails
due to an active OLM-connection on the shared OSA-adapter.

Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>