Remove global var for wireless power, add wl channel menu

NuEVI/midi.cpp

@@ -163,4 +163,20 @@ void sendWLPower(const uint8_t level) {
   buf[5] = level;
   dinMIDIsendSysex(buf, 6);
 
-}
+}
+
+
+void sendWLChannel(const uint8_t channel) {
+  uint8_t buf[6] = {
+    0x00, 0x21, 0x11,  //Manufacturer id
+    0x02,             //TX02
+    0x05,             //Set channel
+    0x04              //Channel value (4-80)
+  };
+
+  if(channel<4 || channel>80) return; //Don't send invalid values
+
+  buf[5] = channel;
+  dinMIDIsendSysex(buf, 6);
+
+}