Use an explicit constant for the source GC time.

route.c

@@ -228,7 +228,7 @@ update_feasible(const unsigned char *a,
     if(src == NULL)
         return 1;
 
-    if(src->time < now.tv_sec - 200)
+    if(src->time < now.tv_sec - SOURCE_GC_TIME)
         /* Never mind what is probably stale data */
         return 1;
 

source.c

@@ -98,7 +98,7 @@ update_source(struct source *src,
     if(metric >= INFINITY)
         return;
 
-    if(src->time < now.tv_sec - 200 ||
+    if(src->time < now.tv_sec - SOURCE_GC_TIME ||
        seqno_compare(src->seqno, seqno) < 0 ||
        (src->seqno == seqno && src->metric > metric)) {
         src->seqno = seqno;

source.h

@@ -20,6 +20,8 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 */
 
+#define SOURCE_GC_TIME 200
+
 struct source {
     unsigned char address[16];
     unsigned char prefix[16];