This change prevents Read from failing with io.EOF, ErrNotImplemented on
exchanging control frames such as ping and pong.

Fixes golang/go#6377.
Fixes golang/go#7825.
Fixes golang/go#10156.

Change-Id: I600cf493de3671d7e3d11e2e12d32f43928b7bfc
Reviewed-on: https://go-review.googlesource.com/13054Reviewed-by: Andrew Gerrand <adg@golang.org>