x/net/websocket: Add the Conn.FrameDataLength and NewClient2

[ruyi789]

Add websocket.NewClient2 to get the http.Response returned by the server, so as to have better countermeasures when there is a handshake error.
Add the websocket.Conn.FrameDataLength method to return the data size of the frame to deal with the read and write logic of the frame.
Added TestNewClient2 test case and usage of FrameDataLength.

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Patch Set 1:

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Message from Damien Neil:

Patch Set 1:

(1 comment)

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