net: rpl: Free received net_buf in case of error
net: rpl: Free received net_buf in case of error

The code did not mark net_buf to be freed in a case of error
when receiving data. This caused the system run out of network
buffers very fast. It is necessary to set uip_len variable to 0 so
that the upper stack can free the buffer in this case.

Change-Id: Id5e009affcb2ce916f21fcf60060efb1c6d1ec0c
Signed-off-by: Jukka Rissanen <f9f077d1da4c7aa947f9864fa5a28c3588f6a45d@linux.intel.com>

explora26/zephyr,fractalclone/zephyr-riscv,kraj/zephyr,galak/zephyr,zephyriot/zephyr,ldts/zephyr,explora26/zephyr,bigdinotech/zephyr,Vudentz/zephyr,aceofall/zephyr-iotos,bboozzoo/zephyr,jamesonwilliams/zephyr-kernel,ldts/zephyr,zephyriot/zephyr,32bitmicro/zephyr,fbsder/zephyr,zephyrproject-rtos/zephyr,coldnew/zephyr-project-fork,finikorg/zephyr,holtmann/zephyr,finikorg/zephyr,kraj/zephyr,tidyjiang8/zephyr-doc,Vudentz/zephyr,ldts/zephyr,galak/zephyr,bboozzoo/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,32bitmicro/zephyr,tidyjiang8/zephyr-doc,sharronliu/zephyr,pklazy/zephyr,pklazy/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,runchip/zephyr-cc3200,aceofall/zephyr-iotos,32bitmicro/zephyr,runchip/zephyr-cc3220,aceofall/zephyr-iotos,explora26/zephyr,fractalclone/zephyr-riscv,runchip/zephyr-cc3220,Vudentz/zephyr,punitvara/zephyr,nashif/zephyr,mbolivar/zephyr,jamesonwilliams/zephyr-kernel,sharronliu/zephyr,holtmann/zephyr,jamesonwilliams/zephyr-kernel,zephyrproject-rtos/zephyr,coldnew/zephyr-project-fork,mbolivar/zephyr,holtmann/zephyr,erwango/zephyr,runchip/zephyr-cc3200,kraj/zephyr,fractalclone/zephyr-riscv,nashif/zephyr,nashif/zephyr,coldnew/zephyr-project-fork,erwango/zephyr,nashif/zephyr,zephyriot/zephyr,zephyrproject-rtos/zephyr,mirzak/zephyr-os,zephyriot/zephyr,fractalclone/zephyr-riscv,GiulianoFranchetto/zephyr,explora26/zephyr,tidyjiang8/zephyr-doc,punitvara/zephyr,galak/zephyr,finikorg/zephyr,rsalveti/zephyr,ldts/zephyr,mirzak/zephyr-os,fbsder/zephyr,mbolivar/zephyr,fbsder/zephyr,punitvara/zephyr,holtmann/zephyr,jamesonwilliams/zephyr-kernel,aceofall/zephyr-iotos,galak/zephyr,pklazy/zephyr,erwango/zephyr,kraj/zephyr,punitvara/zephyr,pklazy/zephyr,explora26/zephyr,fbsder/zephyr,rsalveti/zephyr,mirzak/zephyr-os,jamesonwilliams/zephyr-kernel,ldts/zephyr,mirzak/zephyr-os,sharronliu/zephyr,rsalveti/zephyr,bigdinotech/zephyr,fractalclone/zephyr-riscv,Vudentz/zephyr,erwango/zephyr,bigdinotech/zephyr,erwango/zephyr,tidyjiang8/zephyr-doc,32bitmicro/zephyr,bboozzoo/zephyr,punitvara/zephyr,bigdinotech/zephyr,mirzak/zephyr-os,runchip/zephyr-cc3200,holtmann/zephyr,runchip/zephyr-cc3220,zephyriot/zephyr,rsalveti/zephyr,pklazy/zephyr,GiulianoFranchetto/zephyr,runchip/zephyr-cc3200,mbolivar/zephyr,mbolivar/zephyr,rsalveti/zephyr,bboozzoo/zephyr,aceofall/zephyr-iotos,coldnew/zephyr-project-fork,coldnew/zephyr-project-fork,bigdinotech/zephyr,tidyjiang8/zephyr-doc,32bitmicro/zephyr,runchip/zephyr-cc3200,galak/zephyr,bboozzoo/zephyr,Vudentz/zephyr,Vudentz/zephyr,runchip/zephyr-cc3220,sharronliu/zephyr,fbsder/zephyr,GiulianoFranchetto/zephyr,kraj/zephyr,GiulianoFranchetto/zephyr,runchip/zephyr-cc3220,sharronliu/zephyr,nashif/zephyr