iscsi: Pass the request PDU to icl_conn_transfer_setup().

This matches icl_conn_task_setup() which passes the PDU and avoids the
need for a layering violation in cxgbei to fetch the request PDU from
the ctl_io.

Reviewed by: mav
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D33746