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