net: dns: Fix dns_pack.h documentation of packing routines
net: dns: Fix dns_pack.h documentation of packing routines

Some doxygen directives were missing from dns_pack.h file.
Also make function header documentation look better.

Signed-off-by: Jukka Rissanen <f9f077d1da4c7aa947f9864fa5a28c3588f6a45d@linux.intel.com>

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