net: lwm2m: lower default maximum observes from 20 to 10
net: lwm2m: lower default maximum observes from 20 to 10

In an effort to reduce the footprint of the LwM2M client, let's
lower the default # of observes handled by the client from 20 to
10.

This saves ~640 bytes of SRAM.

Signed-off-by: Michael Scott <17b9e1c64588c7fa6419b4d29dc1f4426279ba01@opensourcefoundries.com>

zephyrproject-rtos/zephyr,explora26/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,Vudentz/zephyr,mbolivar/zephyr,finikorg/zephyr,ldts/zephyr,Vudentz/zephyr,zephyriot/zephyr,galak/zephyr,mbolivar/zephyr,finikorg/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,galak/zephyr,kraj/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr,nashif/zephyr,kraj/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,mbolivar/zephyr,nashif/zephyr,finikorg/zephyr,galak/zephyr,Vudentz/zephyr,zephyriot/zephyr,punitvara/zephyr,galak/zephyr,mbolivar/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,mbolivar/zephyr,nashif/zephyr,zephyriot/zephyr,kraj/zephyr,zephyriot/zephyr,finikorg/zephyr,galak/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,zephyriot/zephyr,explora26/zephyr,explora26/zephyr,kraj/zephyr,Vudentz/zephyr,explora26/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,punitvara/zephyr