net: Remove s_addr/s6_addr defines from in_addr/in6_addr
net: Remove s_addr/s6_addr defines from in_addr/in6_addr

Replace #defines for s_addr/s6_addr etc. in in_addr/in6_addr structures
within net_ip.h with fixed fileds inside an anonymous union. This
prevents intrusive behaviour of net_ip.h, which expands every occurence
of s_addr/s6_addr with it's own define, even in other, non-related
structures.

Signed-off-by: Robert Lubos <9d28997c6894a2d0321a7bb399169af7ce99b64e@nordicsemi.no>

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