[fix] ensure handleUpgrade doesn't break if socket is just a stream

[pimterry]

If you attempt to handle a websocket over a connection that is a stream but not a net.Socket, right now WS fails to do so. With this very small change (very similar to the equivalent handling in Node itself) it's possible to call handleUpgrade with a socket argument that's actually just a duplex stream, and then successfully handle websocket traffic that way.

This can be useful in some cases: in my specific case this is required to proxy WebSockets over non-sockets, such as HTTP/2 streams (note that this is not the same as real WS-over-HTTP/2 support - I receive a proxy CONNECT sent on an HTTP/2 stream, and then the client does an HTTP/1.1 upgrade on that proxied stream, resulting in running an HTTP/1.1 websocket over an HTTP/2 stream instead of a raw socket).

With this change, that works flawlessly for me, proxying real websocket traffic from Chrome in an HTTP/2 proxy.

This is also a small step towards #1458, since the same change will also eventually be required to add full HTTP/2 support, where the entire underlying connection is HTTP/2 throughout, with no proxying involved.

(Arguably the same could be done for the socket.setTimeout above too, but in my case that doesn't seem to be required, and I wanted to avoid changing anything else unnecessarily).

[lpinca]

Nits:

Suggested change

	// May not be available if 'socket' is actually a stream
	//
	// May not be available if `socket` is actually a stream.
	//

[lpinca]

Why the same is not needed for socket.setTimeout()? I also wonder if it is possible to add a test.

[pimterry]

For setTimeout, my reasoning is in the description:

(Arguably the same could be done for the socket.setTimeout above too, but in my case that doesn't seem to be required, and I wanted to avoid changing anything else unnecessarily).

Happy to change it though, it works for me either way!

I've just pushed a commit to cover setTimeout too, apply your nit suggestion, and add a separate test to cover this (which fails without this change, but now passes & works correctly).

[lpinca]

Thank you.