Before, if a graceful shutdown was triggered while the handshake was in-progress, the connection would just be dropped instantly. However, if some requests were in-flight as part of the handshake, they'd get dropped along with it.

Now, if handshake is in-progress, we record that a close is desired, and as soon as the handshake has completed, the real graceful shutdown process starts, which should send the proper signals back about what happened with the in-flight requests.

The patch #3528 added the ability for hyper users to configure
`max_local_error_reset_streams` via the server builder to hyper
v0.14.29. It was then pulled in to hyper v1.2.0 as well in #3530, where
the wrong parameter `max_pending_accept_reset_streams` is passed to h2's
builder as `max_local_error_reset_streams`.

This could lead to significant impact especially when a hyper user does
not set `max_pending_accept_reset_streams`, because its default value is
`None` and passing `None` to h2's `max_local_error_reset_streams` method
will make the server vulnerable to DOS attacks.

This issue has been fixed in this patch, simply by passing the correct
value to the h2's builder method.