cxgbe: Move send_iscsi_flowc_wr to t4_tom.ko
Rename the function to send_txdataplen_max_flowc_wr to match the
parameter it sets. This function will be reused by other ULP modules.
Sponsored by: Chelsio Communications
(cherry picked from commit 35b883ccf36521a46ba1cd959c144328cce223c5)