net.server_epoll: Refactor immediate TLS handshake start

net.server_epoll: Keep socket registered in epoll trough TLS wrapping There's the theory that the socket isn't the same before/after wrap(), but since epoll operates on FD numbers this shouldn't matter.

net.server_epoll: Use TLS handshake timeout after initiating handshake The :init() method sets a different timeout than the TLS related methods.

net.server_epoll: Start TLS handshake immediately on newly accepted connections Since TLS is a client-first protocol there is a chance that the ClientHello message is available already. TLS Fast Open and/or the TCP_DEFER_ACCEPT socket option would increase that chance.

net.server_epoll: Factor out TLS initialization into a method So there's :startls(), :inittls() and :tlshandshake() :starttls() prepares for plain -> TLS upgrade and ensures that the (unencrypted) write buffer is drained before proceeding. :inittls() wraps the connection and does things like SNI, DANE etc. :tlshandshake() steps the TLS negotiation forward until it completes

net.server_epoll: Fix typo

mod_s2s: Log debug message on attempted close of an connectionless session This should probably never happen, but probably does anyways. A debug message would show the truth of the matter.

mod_s2s: Drop level of indentation by inverting a condition and early return Nicer to get rid of a conditional that covers such a large portion of a pretty big function.

mod_s2s: Use module API to fire events These direct accesses are probably more optimized, but weird when the module API has methods for these things.

scansion tests: Allow specifying network settings via environment variable Allows testing e.g. opportunistic writes or other settings easily in CI or otherwise without editing the config file. make integration-test PROSODY_NETWORK_SETTINGS='{"opportunistic_writes":true}'