keep rf95 max power at 20 dBm so users don't smoke their boards

src/mesh/RF95Interface.cpp

@@ -3,7 +3,7 @@
 #include "RadioLibRF95.h"
 #include <configuration.h>
 
-#define MAX_POWER 27
+#define MAX_POWER 20
 // if we use 20 we are limited to 1% duty cycle or hw might overheat.  For continuous operation set a limit of 17
 // In theory up to 27 dBm is possible, but the modules installed in most radios can cope with a max of 20.  So BIG WARNING
 // if you set power to something higher than 17 or 20 you might fry your board.