Add reselectdist command

sources.h

@@ -140,6 +140,9 @@ extern void SRC_SelectSource(unsigned long match_addr);
 /* Force reselecting the best source */
 extern void SRC_ReselectSource(void);
 
+/* Set reselect distance */
+extern void SRC_SetReselectDistance(double distance);
+
 /* Predict the offset of the local clock relative to a given source at
    a given local cooked time. Positive indicates local clock is FAST
    relative to reference. */