Move the declaration of bandwidth_rate_rule_to_string

It's natural for the definition of bandwidth_rule_t to be with the functions
that actually care about its values.  Unfortunately, this means declaring
bandwidth_rate_rule_to_string() out of sequence.  Someday we'll just rename
reasons.c to strings.c, and put it at the end of or.h, and this will all be
better.

changes/move_bwrts_declaration

@@ -0,0 +1,2 @@
+  o Minor bugfixes:
+    - Fix a compilation warning in or.h related to bandwidth_weight_rule_t

src/or/or.h

@@ -4493,9 +4493,6 @@ const char *circuit_end_reason_to_control_string(int reason);
 const char *socks4_response_code_to_string(uint8_t code);
 const char *socks5_response_code_to_string(uint8_t code);
 
-enum bandwidth_weight_rule_t;
-const char *bandwidth_weight_rule_to_string(enum bandwidth_weight_rule_t rule);
-
 /********************************* relay.c ***************************/
 
 extern uint64_t stats_n_relay_cells_relayed;
@@ -4975,6 +4972,9 @@ routerinfo_t *routerlist_sl_choose_by_bandwidth(smartlist_t *sl,
 routerstatus_t *routerstatus_sl_choose_by_bandwidth(smartlist_t *sl,
                                                 bandwidth_weight_rule_t rule);
 
+/* XXXX actually declared in reasons.c */
+const char *bandwidth_weight_rule_to_string(enum bandwidth_weight_rule_t rule);
+
 /** Flags to be passed to control router_choose_random_node() to indicate what
  * kind of nodes to pick according to what algorithm. */
 typedef enum {