BUG/MINOR: http: fix "set-tos" not working in certain configurations

s->req->prod->conn->addr.to.ss_family contains only useful data if
conn_get_to_addr() is called early. If thats not the case (nothing in the
configuration needs the destination address like logs, transparent, ...)
then "set-tos" doesn't work.

Fix this by checking s->req->prod->conn->addr.from.ss_family instead.
Also fix a minor doc issue about set-tos in http-response.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index dddb07e..675bb8e 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -2803,7 +2803,8 @@
 
 http-response { allow | deny | add-header <name> <fmt> | set-nice <nice> |
                 set-header <name> <fmt> | set-log-level <level> |
-                set-mark <mark> } [ { if | unless } <condition> ]
+                set-mark <mark> | set-tos <tos> }
+              [ { if | unless } <condition> ]
   Access control for Layer 7 responses
 
   May be used in sections:   defaults | frontend | listen | backend