Add flush_resends.

This function does nothing right now, it will be used when we learn to resend
unicast packets.

resend.c

@@ -44,6 +44,12 @@ resend_match(struct resend *resend,
             resend->plen == plen && memcmp(resend->prefix, prefix, 16) == 0);
 }
 
+void
+flush_resends(struct neighbour *neigh)
+{
+    /* Nothing for now */
+}
+
 static struct resend *
 find_resend(int kind, const unsigned char *prefix, unsigned char plen,
              struct resend **previous_return)

resend.h

@@ -43,6 +43,7 @@ extern struct timeval resend_time;
 
 struct resend *find_request(const unsigned char *prefix, unsigned char plen,
                             struct resend **previous_return);
+void flush_resends(struct neighbour *neigh);
 int record_resend(int kind, const unsigned char *prefix, unsigned char plen,
                    unsigned short seqno, unsigned short router_hash,
                    struct network *net, int delay);