Don't use RESET_N pin (#550)

Data sheet discourages use of SARA modem reset pin, use may lead to irrecoverable state of modem

Author: janakelarsson

variants/mkrnb1500/variant.cpp

@@ -252,7 +252,8 @@ void initVariant() {
   pinMode(SARA_PWR_ON, OUTPUT);
   digitalWrite(SARA_PWR_ON, LOW);
 
-  // put SARA modem in reset on start to conserve power if it's not used
+  // data sheet discourages use of SARA modem reset pin
+  // use may lead to irrecoverable state of modem
   pinMode(SARA_RESETN, OUTPUT);
   digitalWrite(SARA_RESETN, LOW);