libwebsockets

lws_ss_change_handlers: allow dynamic handler change

You may use separate rx or tx handlers to neatly isolate different
rx or tx state handling, for example if the connection enters some
mode where you may send a variety of possibly large things, it can
be advantageous to have different code handling each of the
different things.

This allows you to change the rx, tx and / or state handlers to
different ones suitable for the user protocol state, if it's helpful.

With upcoming SS Server support, this has another use when SS
indicates that the underlying protocol upgraded, eg, http -> ws,
you may want to change the handlers for the different sort of
payloads expected after that, according to your user protocol.