net/http: Show more data for unsolicited response

Show more than one character when we recieve a unsolicited
response on an idle HTTP channel. Showing more than one
byte is really useful when you want to debug your program
when you get this message.

Change-Id: I3caf9f06420e7c2a2de3e4eb302c5dab95428fdb
Reviewed-on: https://go-review.googlesource.com/13959
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/transport.go

@@ -925,8 +925,8 @@ func (pc *persistConn) readLoop() {
 			if !pc.closed {
 				pc.closeLocked()
 				if len(pb) > 0 {
-					log.Printf("Unsolicited response received on idle HTTP channel starting with %q; err=%v",
-						string(pb), err)
+					buf, _ := pc.br.Peek(pc.br.Buffered())
+					log.Printf("Unsolicited response received on idle HTTP channel starting with %q; err=%v", buf, err)
 				}
 			}
 			pc.lk.Unlock()