Added RDS filter option

You can now select RDS filter on/off in the menu.

Off: RDS data can be dirty, but is very fast.

On: RDS data is buffered and filtered by the TEF668x.

src/TEF6686.h

@@ -193,6 +193,7 @@ typedef struct _rds_ {
   bool hasCT;
   bool rtAB;
   bool correct;
+  bool filter;
   bool underscore;
   bool rdsreset;
 } rds_;