http2: correctly wrap ErrFrameTooLarge in Framer.ReadFrame

In Framer.ReadFrame's frame-too-large check, the code that checks for
HTTP/1.1 looking frames accidentally wrapped the unrelated err from the
previous readFrameHeader call instead of ErrFrameTooLarge. Fix that.

Change-Id: I2237759eaad8c6e06e7195c50410abb5792e57ea
Reviewed-on: https://go-review.googlesource.com/c/net/+/676218
Reviewed-by: Chressie Himpel <[email protected]>
Reviewed-by: Damien Neil <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: chressie

http2/frame.go

@@ -509,7 +509,7 @@ func (fr *Framer) ReadFrame() (Frame, error) {
 	}
 	if fh.Length > fr.maxReadSize {
 		if fh == invalidHTTP1LookingFrameHeader() {
-			return nil, fmt.Errorf("http2: failed reading the frame payload: %w, note that the frame header looked like an HTTP/1.1 header", err)
+			return nil, fmt.Errorf("http2: failed reading the frame payload: %w, note that the frame header looked like an HTTP/1.1 header", ErrFrameTooLarge)
 		}
 		return nil, ErrFrameTooLarge
 	}