Eliminated inefficient serial function calls at runtime.

src/main/msp/msp_serial.h

@@ -96,6 +96,7 @@ typedef struct __attribute__((packed)) {
 struct serialPort_s;
 typedef struct mspPort_s {
     struct serialPort_s *port; // null when port unused.
+    bool sharedWithTelemetry;
     timeMs_t lastActivityMs;
     mspPendingSystemRequest_e pendingRequest;
     mspState_e c_state;