cnic: Improve ->iscsi_nl_msg_send()

1. Change first parameter from cnic_dev to ulp_handle which is the hba
pointer.  All other similar upcalls are using hba pointer.  The callee
can then directly reference the hba without conversion.

2. Change return value from void to int so that an error code can be
passed back.  This allows the operation to be retried.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>