net/icmpv4: Rename static function with icmpv4_ prefix
net/icmpv4: Rename static function with icmpv4_ prefix

Static ones with that prefix, exported ones with net_icmpv4_ prefix.

Fixes #8720

Signed-off-by: Tomasz Bursztyka <ba81a3a719836727e6857ae83462b9f52ec41006@linux.intel.com>

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