nbIOT_test sketch adaption

using firmware 6.57 on aublox SARA-N211, i needed to adapt the example sketch with extra doublequotes to get things working:

const char* cdp = "\"\""; 

Doing this in a backwards compatible way may require getting the firmware version results from AT+CGMR and based on the response, set the string. This is left as an exercise to the reader :slight_smile: