internal/http3: fix wrong argument being given when validating header value

Change-Id: I04eb0db74bfe677829d06623ec3ab77d6a6a6964
Reviewed-on: https://go-review.googlesource.com/c/net/+/788880
Reviewed-by: Damien Neil <dneil@google.com>
Auto-Submit: Nicholas Husin <husin@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Nicholas Husin <husin@google.com>

internal/http3/body.go

diff --git a/internal/http3/body.go b/internal/http3/body.go
index ac95909..f226550 100644
--- a/internal/http3/body.go
+++ b/internal/http3/body.go
@@ -194,7 +194,7 @@
 				if r.trailer == nil {
 					return nil
 				}
-				if !validWireHeaderFieldName(name) || !httpguts.ValidHeaderFieldValue(name) {
+				if !validWireHeaderFieldName(name) || !httpguts.ValidHeaderFieldValue(value) {
 					return nil
 				}
 				name = textproto.CanonicalMIMEHeaderKey(textproto.TrimString(name))