net/af_iucv: support drop monitoring

Change the good paths to use consume_skb() instead of kfree_skb(). This
avoids flooding dropwatch with false-positives.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>