This removes RequireHandshakeHybrid support and changes the default behavior
to RequireHandshakeOn. Dial calls will now block and wait for a successful
handshake before proceeding. Users relying on the old hybrid behavior (cmux
users) should consult https://github.com/soheilhy/cmux/issues/64.
Also, several tests have been updated to take this into consideration by
sending settings frames.
New connections can race with GracefulStop such that the server will accept the connection, but then close it immediately. If a connection is accepted before GracefulStop has a chance to effectively cancel the listeners, the server should handle it to avoid client errors.
