netiucv: improve state checking in conn_action_txdone

state checking in conn_action_txdone() is inconsistent.
This patch makes it consistent and issues a trace message
if an unexpected state is detected for the netiucv device.

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>