doc: relnotes-1.13: Condense/cleanup networking section
doc: relnotes-1.13: Condense/cleanup networking section

Merged closely related items into one bullet point, improve
description of some items, try to sort items a bit better
(that can be further improved).

Signed-off-by: Paul Sokolovsky <35cb557f011771c94f127d6fef99f804b62203f5@linaro.org>

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