cxgbe tom: Permit rcv_nxt mismatches on FIN for iSCSI connections on T6.

The remote peer might send a FIN in the middle of a burst of data
PDUs. In the case of T6 with data PDU completion moderation, the
driver would not have seen these PDUs since the final PDU in the burst
was never received resulting in a stale rcv_nxt when the FIN is
received.

While here, invert the logic in the condition to be more readable and
always set tp->rcv_nxt from the sequence number in the CPL. This sets
the proper value of rcv_nxt for FINs on connections with data received
but not reported via a CPL (e.g. a partial iSCSI PDU burst interrupted
by a FIN).

Reported by: Jithesh Arakkan @ Chelsio
Reviewed by: np
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D30871

(cherry picked from commit d59f1c49e26ba29e7583019bb5d6aa029466fdb6)

cxgbe tom: Update rcv_nxt for a FIN after handle_ddp_close().

For TCP DDP, handle_ddp_close() needs to see the pre-FIN rcv_nxt to
determine how much data was placed in the local buffer before the FIN
was received. The changes in d59f1c49e26b broke this by updating
rcv_nxt before calling handle_ddp_close().

Fixes: d59f1c49e26b cxgbe tom: Permit rcv_nxt mismatches on FIN for iSCSI connections on T6.
Sponsored by: Chelsio Communications

(cherry picked from commit 5dbf8c1588da167c17c45bdf78de51fcb4929504)