net: lwm2m: return BAD_REQUEST when object create fails
net: lwm2m: return BAD_REQUEST when object create fails

Per LwM2M spec (7.3.2.4 Operation on Object):
"If the payload (New Value) conveys an Object Instance ID in conflict
with one already present in the LwM2M Client, the complete request
MUST be rejected and a "Bad Request" error code MUST be sent back."

Let's do that.

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

punitvara/zephyr,aceofall/zephyr-iotos,ldts/zephyr,fbsder/zephyr,kraj/zephyr,explora26/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,runchip/zephyr-cc3220,galak/zephyr,zephyriot/zephyr,galak/zephyr,zephyriot/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,runchip/zephyr-cc3220,mbolivar/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,mbolivar/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,aceofall/zephyr-iotos,punitvara/zephyr,punitvara/zephyr,ldts/zephyr,aceofall/zephyr-iotos,galak/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,fbsder/zephyr,aceofall/zephyr-iotos,ldts/zephyr,fbsder/zephyr,nashif/zephyr,fbsder/zephyr,punitvara/zephyr,Vudentz/zephyr,zephyriot/zephyr,runchip/zephyr-cc3220,punitvara/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,runchip/zephyr-cc3220,kraj/zephyr,GiulianoFranchetto/zephyr,kraj/zephyr,nashif/zephyr,Vudentz/zephyr,explora26/zephyr,ldts/zephyr,kraj/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,mbolivar/zephyr,mbolivar/zephyr,zephyriot/zephyr,fbsder/zephyr,kraj/zephyr,galak/zephyr,mbolivar/zephyr,zephyriot/zephyr,Vudentz/zephyr,runchip/zephyr-cc3220,aceofall/zephyr-iotos,galak/zephyr