net: tcp: if buffer is TCP_FIN increment send_ack by 1
net: tcp: if buffer is TCP_FIN increment send_ack by 1

Now that the TCP_FIN block is after a potential packet_received()
tcp->send_ack should be appropriately set to the last sequence
processed.

In the case of a TCP_FIN buffer, we should advance it by 1 or else
the destination will continue to retry to send the last block.

Change-Id: I9c97d35a87ad6cc1a50f928b237780bff4cd2877
Signed-off-by: Michael Scott <087571639a1dbb4ff1803c64e3643475ba482686@linaro.org>

holtmann/zephyr,fbsder/zephyr,sharronliu/zephyr,zephyrproject-rtos/zephyr,fractalclone/zephyr-riscv,mbolivar/zephyr,zephyriot/zephyr,finikorg/zephyr,fractalclone/zephyr-riscv,Vudentz/zephyr,zephyrproject-rtos/zephyr,aceofall/zephyr-iotos,bboozzoo/zephyr,finikorg/zephyr,punitvara/zephyr,kraj/zephyr,rsalveti/zephyr,punitvara/zephyr,galak/zephyr,pklazy/zephyr,fbsder/zephyr,explora26/zephyr,bigdinotech/zephyr,kraj/zephyr,aceofall/zephyr-iotos,bigdinotech/zephyr,runchip/zephyr-cc3200,sharronliu/zephyr,runchip/zephyr-cc3220,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,erwango/zephyr,holtmann/zephyr,fbsder/zephyr,runchip/zephyr-cc3220,erwango/zephyr,fractalclone/zephyr-riscv,sharronliu/zephyr,GiulianoFranchetto/zephyr,fractalclone/zephyr-riscv,fbsder/zephyr,pklazy/zephyr,zephyriot/zephyr,zephyrproject-rtos/zephyr,holtmann/zephyr,Vudentz/zephyr,nashif/zephyr,rsalveti/zephyr,nashif/zephyr,finikorg/zephyr,runchip/zephyr-cc3220,pklazy/zephyr,runchip/zephyr-cc3200,pklazy/zephyr,ldts/zephyr,erwango/zephyr,kraj/zephyr,sharronliu/zephyr,mbolivar/zephyr,galak/zephyr,pklazy/zephyr,runchip/zephyr-cc3200,bboozzoo/zephyr,runchip/zephyr-cc3220,bboozzoo/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,bigdinotech/zephyr,sharronliu/zephyr,tidyjiang8/zephyr-doc,holtmann/zephyr,mbolivar/zephyr,ldts/zephyr,bboozzoo/zephyr,explora26/zephyr,zephyriot/zephyr,aceofall/zephyr-iotos,GiulianoFranchetto/zephyr,Vudentz/zephyr,runchip/zephyr-cc3200,nashif/zephyr,kraj/zephyr,fractalclone/zephyr-riscv,mbolivar/zephyr,bigdinotech/zephyr,holtmann/zephyr,Vudentz/zephyr,rsalveti/zephyr,nashif/zephyr,galak/zephyr,nashif/zephyr,rsalveti/zephyr,galak/zephyr,punitvara/zephyr,aceofall/zephyr-iotos,ldts/zephyr,bigdinotech/zephyr,punitvara/zephyr,finikorg/zephyr,galak/zephyr,runchip/zephyr-cc3220,tidyjiang8/zephyr-doc,erwango/zephyr,tidyjiang8/zephyr-doc,explora26/zephyr,runchip/zephyr-cc3200,tidyjiang8/zephyr-doc,punitvara/zephyr,zephyriot/zephyr,ldts/zephyr,finikorg/zephyr,fbsder/zephyr,zephyrproject-rtos/zephyr,rsalveti/zephyr,zephyriot/zephyr,erwango/zephyr,mbolivar/zephyr,Vudentz/zephyr,kraj/zephyr,aceofall/zephyr-iotos,ldts/zephyr,tidyjiang8/zephyr-doc,explora26/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,bboozzoo/zephyr