samples: net: irc-bot: fix cmd parsing across multiple buffers
samples: net: irc-bot: fix cmd parsing across multiple buffers

Let's simplify the parsing function which scans incoming traffic
for carriage returns and let the net_pkt_read() function cross
multiple buffers if needed.  Also, gracefully skip lines which
are longer than the command buffer.

Signed-off-by: Michael Scott <087571639a1dbb4ff1803c64e3643475ba482686@linaro.org>

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