on_pre_open: add ip to the handler

[BV-WebDev]

Related to uWS.js issue 1257.
Allows the IP to be exported in addition to the FD.

[uNetworkingAB]

You also need to change the adopt socket call to pass along the IP to on_open

[BV-WebDev]

adopt_accepted_socket calls were already passing IP along to the open handler.
I have tested these in JS and it seems to work. Do you see anything missing?

Changes summary:
uSockets: add the IP to the pre_open handler.
uWS: pass the IP to the pre_open handler.
uWS: update adoptSocket() to accept an optional IP parameter and pass it to uSockets.
uWS: update LocalCluster and addChildApp() to retrieve the IP on pre_open and pass it to adoptSocket().
uWS.js: update adoptSocket() to accept an optional IP parameter.

If someone accepts external FD, needs the IP on the request and uses the UWS_REMOTE_ADDRESS_USERSPACE cache, they have to pass the IP to adoptSocket().

[uNetworkingAB]

If someone accepts external FD, needs the IP on the request and uses the UWS_REMOTE_ADDRESS_USERSPACE cache, they have to pass the IP to adoptSocket().

That's okay they can get it from the FD before they pass it