net: contiki: Fix the RA ICMPv6 sending
net: contiki: Fix the RA ICMPv6 sending

The ICMPv6 RA payload was ignored and not sent. This was seen
as malformed packet by receiver. We must update the length of
the message by calling net_buf_add().

Change-Id: I3dc64cfce669de54283db290cfb009b2c6ea7225
Signed-off-by: Jukka Rissanen <f9f077d1da4c7aa947f9864fa5a28c3588f6a45d@linux.intel.com>

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