rend: stop warning when clients send multiple rend establish cells

Stop logging "Tried to establish rendezvous on non-OR circuit..." as
a warning. Instead, log it as a protocol warning, because there is
nothing that relay operators can do to fix it.

Fixes bug 29029; bugfix on 0.2.5.7-rc.

changes/bug29029

@@ -0,0 +1,5 @@
+  o Minor bugfixes (logging, onion services):
+    - Stop logging "Tried to establish rendezvous on non-OR circuit..." as
+      a warning. Instead, log it as a protocol warning, because there is
+      nothing that relay operators can do to fix it. Fixes bug 29029;
+      bugfix on 0.2.5.7-rc.

src/or/rendmid.c

@@ -242,9 +242,9 @@ rend_mid_establish_rendezvous(or_circuit_t *circ, const uint8_t *request,
            (unsigned)circ->p_circ_id);
 
   if (circ->base_.purpose != CIRCUIT_PURPOSE_OR) {
-    log_warn(LD_PROTOCOL,
-             "Tried to establish rendezvous on non-OR circuit with purpose %s",
-             circuit_purpose_to_string(circ->base_.purpose));
+    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+           "Tried to establish rendezvous on non-OR circuit with purpose %s",
+           circuit_purpose_to_string(circ->base_.purpose));
     goto err;
   }