Add has_wifi for sacha

https://github.com/meshtastic/Meshtastic-device/issues/979

mesh.proto

@@ -962,6 +962,12 @@ message MyNodeInfo {
    */
   repeated uint32 air_period_rx = 17;
 
+  /*
+   * Is the device wifi capable?
+   */
+   bool has_wifi = 18;
+
+
   /*
    * FIXME - add more useful debugging state (queue depths etc)
    */