Discard circuit paths on which nobody supports ntor

Right now this accounts for about 1% of circuits over all, but if you
pick a guard that's running 0.2.3, it will be about 6% of the circuits
running through that guard.

Making sure that every circuit has at least one ntor link means that
we're getting plausibly good forward secrecy on every circuit.

This implements ticket 9777,

1 files changed, 1 insertions, 0 deletions

diff --git a/src/or/circuitlist.h b/src/or/circuitlist.h
index 874f68cd22..acc4b81fcd 100644
--- a/src/or/circuitlist.h
+++ b/src/or/circuitlist.h
@@ -50,6 +50,7 @@ void circuit_mark_all_dirty_circs_as_unusable(void);
 void circuit_mark_for_close_(circuit_t *circ, int reason,
                              int line, const char *file);
 int circuit_get_cpath_len(origin_circuit_t *circ);
+void circuit_clear_cpath(origin_circuit_t *circ);
 crypt_path_t *circuit_get_cpath_hop(origin_circuit_t *circ, int hopnum);
 void circuit_get_all_pending_on_channel(smartlist_t *out,
                                         channel_t *chan);