Log calls http_ForceField() in VSL using xxxUnset

Previously we would force the protocol and method fields to HTTP/1.1 and
GET, respectively, but hide this from VSL showing 2 different entries
for BereqProtocol and/or BereqMethod.

Discussed with arianna@.

Fixes #1662

bin/varnishd/cache/cache_http.c

@@ -752,11 +752,17 @@ http_GetMethod(const struct http *hp)
 void
 http_ForceField(const struct http *to, unsigned n, const char *t)
 {
+	int i;
+
 	CHECK_OBJ_NOTNULL(to, HTTP_MAGIC);
 	assert(n < HTTP_HDR_FIRST);
 	AN(t);
-	if (to->hd[n].b == NULL || strcmp(to->hd[n].b, t))
+	if (to->hd[n].b == NULL || strcmp(to->hd[n].b, t)) {
+		i = (HTTP_HDR_UNSET - HTTP_HDR_METHOD);
+		i += to->logtag;
+		VSLbt(to->vsl, (enum VSL_tag_e)i, to->hd[n]);
 		http_SetH(to, n, t);
+	}
 }
 
 /*--------------------------------------------------------------------*/

bin/varnishtest/tests/r01662.vtc

+varnishtest "Unhide http_ForceField() calls in VSL"
+
+server s1 {
+	rxreq
+	expect req.method == "GET"
+	expect req.proto == "HTTP/1.1"
+	txresp
+} -start
+
+varnish v1 -vcl+backend {
+} -start
+
+logexpect l1 -v v1 -g request {
+	expect * 1001	ReqMethod	"HEAD"
+	expect * =	ReqProtocol	"HTTP/1.0"
+	expect * 1002	BereqUnset	"HEAD"
+	expect 0 =	BereqMethod	"GET"
+	expect * =	BereqUnset	"HTTP/1.0"
+	expect 0 =	BereqProtocol	"HTTP/1.1"
+} -start
+
+client c1 {
+	txreq -req HEAD -proto HTTP/1.0
+	rxresp
+} -run
+
+logexpect l1 -wait