Add RTL VFO bandwidth options

Add RTL VFO bandwidth options
-Y 8 for 8 kHz VFO
-Y 24 for 24 kHz VFO

Should work at any interval where 48 cleanly divides by a number

include/dsd.h

@@ -142,6 +142,7 @@ typedef struct
   int rtl_squelch_level;
   int rtl_volume_multiplier;
   int rtl_udp_port;
+  int rtl_bandwidth;
   int monitor_input_audio;
 } dsd_opts;