Expose get_unique_circ_id_by_chan() to test suite

src/or/circuitbuild.c

@@ -14,6 +14,7 @@
 #include "or.h"
 #include "channel.h"
 #include "circpathbias.h"
+#define CIRCUITBUILD_PRIVATE
 #include "circuitbuild.h"
 #include "circuitlist.h"
 #include "circuitstats.h"