af_iucv: get rid of state IUCV_SEVERED

af_iucv differs unnecessarily between state IUCV_SEVERED and
IUCV_DISCONN. This patch removes state IUCV_SEVERED.
While simplifying af_iucv, this patch removes the 2nd invocation of
cpcmd as well.

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>