RDS: TCP: set RDS_FLAG_RETRANSMITTED in cp_retrans list

As noted in rds_recv_incoming() sequence numbers on data packets
can decreas for the failover case, and the Rx path is equipped
to recover from this, if the RDS_FLAG_RETRANSMITTED is set
on the rds header of an incoming message with a suspect sequence
number.

The RDS_FLAG_RETRANSMITTED is predicated on the RDS_FLAG_RETRANSMITTED
flag in the rds_message, so make sure the flag is set on messages
queued for retransmission.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>