DOC: Update doc about weight, act and bck fields in the statistics

Reorder description of the mentioned fields in order to match the
order of types
(cherry picked from commit 1f673c72c11d011bbd24e309d3155384eddf7a46)
diff --git a/doc/configuration.txt b/doc/configuration.txt
index a9d497e..6f5eeb1 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -13240,9 +13240,9 @@
      server. The server value counts the number of times that server was
      switched away from.
  17. status [LFBS]: status (UP/DOWN/NOLB/MAINT/MAINT(via)...)
- 18. weight [..BS]: server weight (server), total weight (backend)
- 19. act [..BS]: server is active (server), number of active servers (backend)
- 20. bck [..BS]: server is backup (server), number of backup servers (backend)
+ 18. weight [..BS]: total weight (backend), server weight (server)
+ 19. act [..BS]: number of active servers (backend), server is active (server)
+ 20. bck [..BS]: number of backup servers (backend), server is backup (server)
  21. chkfail [...S]: number of failed checks. (Only counts checks failed when
      the server is up.)
  22. chkdown [..BS]: number of UP->DOWN transitions. The backend counter counts