net: lib: lwm2m: fix coap proxy resource option
net: lib: lwm2m: fix coap proxy resource option

commit 2a7546fb5ae9 ("net: lwm2m: add support for coap2coap proxy")
erroneously changed the COAP_OPTION_* used to specify the coap2coap
or coap2http proxy resource used from COAP_OPTION_URI_PATH to
COAP_OPTION_PROXY_SCHEME.

Changing it back to COAP_OPTION_URI_PATH requires us to re-order how
the coap options are appended to the packet as the coap options must
be added in the order specified by the numbers in:
https://tools.ietf.org/html/rfc7252#section-12.2

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

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