Add cli config flood.advert.base

0 = forwarding flood adverts off
1 = forwarding flood adverts on (unrestricted)
0.308 (default) = prob. forwarding according to #1338

src/helpers/CommonCLI.h

@@ -36,6 +36,7 @@ struct NodePrefs { // persisted to file
   uint8_t flood_max;
   uint8_t interference_threshold;
   uint8_t agc_reset_interval; // secs / 4
+  float flood_advert_base;
   // Bridge settings
   uint8_t bridge_enabled; // boolean
   uint16_t bridge_delay;  // milliseconds (default 500 ms)