REGTEST: add an extra testcase for ifnone-forwardfor

In GH #2187 it was mentioned that the ifnone-forwardfor regtest
did not cover the case where forwardfor ifnone is explicitly set in
the frontend but forwardfor option is not used in the backend.

Expected behavior in this case is that the frontend takes the precedence
because the backend did not specify the option.

Adding this missing case to prevent regressions in the future.

reg-tests/http-rules/ifnone-forwardfor.vtc

@@ -24,6 +24,7 @@ haproxy h1 -conf {
 	option forwardfor if-none
 	use_backend be1 if { path /req1 }
 	use_backend be2 if { path /req2 }
+	use_backend be3 if { path /req3 }
 
     frontend normal
         bind "fd@${normal}"
@@ -44,6 +45,9 @@ haproxy h1 -conf {
     backend be2
         option forwardfor if-none
         server s1 ${h1_fe2_addr}:${h1_fe2_port}
+
+    backend be3
+        server s1 ${h1_fe2_addr}:${h1_fe2_port}
 } -start
 
 client c1 -connect ${h1_none_sock} {
@@ -67,6 +71,13 @@ client c1 -connect ${h1_none_sock} {
     expect resp.status == 200
     expect resp.http.x-ff == 1
 
+    txreq -req GET -url /req3 \
+        -hdr "x-src: 10.0.0.128" \
+        -hdr "x-forwarded-for: 127.0.0.1"
+    rxresp
+    expect resp.status == 200
+    expect resp.http.x-ff == 1
+
 } -run
 
 client c1 -connect ${h1_normal_sock} {