repair: fix fd_repair_send_sign_request map index for pong

Author: two-heart

src/discof/repair/fd_repair_tile.c

@@ -64,6 +64,7 @@
 
 /* static map from request type to metric array index */
 static uint metric_index[FD_REPAIR_KIND_ORPHAN + 1] = {
+  [FD_REPAIR_KIND_PONG]          = FD_METRICS_ENUM_REPAIR_SENT_REQUEST_TYPES_V_PONG_IDX,
   [FD_REPAIR_KIND_SHRED]         = FD_METRICS_ENUM_REPAIR_SENT_REQUEST_TYPES_V_NEEDED_WINDOW_IDX,
   [FD_REPAIR_KIND_HIGHEST_SHRED] = FD_METRICS_ENUM_REPAIR_SENT_REQUEST_TYPES_V_NEEDED_HIGHEST_WINDOW_IDX,
   [FD_REPAIR_KIND_ORPHAN]        = FD_METRICS_ENUM_REPAIR_SENT_REQUEST_TYPES_V_NEEDED_ORPHAN_IDX,