MINOR: stream: add timeout sample fetches

Add cur_server_timeout and cur_tunnel_timeout.

These sample fetches return the current timeout value for a stream. This
is useful to retrieve the value of a timeout which was changed via a
set-timeout rule.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 8d5a7d2..7de7087 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -16865,6 +16865,16 @@
   current backend. This timeout can be overwritten by a "set-timeout" rule. See
   also the "cur_tunnel_timeout".
 
+cur_server_timeout : integer
+  Returns the currently applied server timeout in millisecond for the stream.
+  In the default case, this will be equal to be_server_timeout unless a
+  "set-timeout" rule has been applied. See also "be_server_timeout".
+
+cur_tunnel_timeout : integer
+  Returns the currently applied tunnel timeout in millisecond for the stream.
+  In the default case, this will be equal to be_tunnel_timeout unless a
+  "set-timeout" rule has been applied. See also "be_tunnel_timeout".
+
 dst : ip
   This is the destination IPv4 address of the connection on the client side,
   which is the address the client connected to. It can be useful when running