Previously handlers were mandatory.  However they are not always needed.
For example, a server configured with ssl_reject_handshake does not need a
handler.  Such servers required a fake handler to pass the check.  Now handler
absence check is moved to runtime.  If handler is missing, the connection is
closed with 500 code.

The move makes the code look similar to the corresponding code in http module.

The FreeBSD SO_SETFIB support.

The FreeBSD accept filters support.

The Linux TCP_DEFER_ACCEPT support.

Server name is taken either from ngx_stream_ssl_module or
ngx_stream_ssl_preread_module.

The change adds "default_server" parameter to the "listen" directive,
as well as the following directives: "server_names_hash_max_size",
"server_names_hash_bucket_size", "server_name" and "ssl_reject_handshake".

Previously, preread buffer was always read out from socket, which made it
impossible to terminate SSL on the connection without introducing additional
SSL BIOs.  The following patches will rely on this.

Now, when possible, recv(MSG_PEEK) is used instead, which keeps data in socket.
It's called if SSL is not already terminated and if an egde-triggered event
method is used.  For epoll, EPOLLRDHUP support is also required.

Ports difference must be respected when checking addresses for duplicates,
otherwise configurations like this are broken:

  listen 127.0.0.1:6000-6005

It was broken by 4cc2bfeff46c (nginx 1.23.3).

Due to the glibc bug[1], getaddrinfo("localhost") with AI_ADDRCONFIG
on a typical host with glibc and without IPv6 returns two 127.0.0.1
addresses, and therefore "listen localhost:80;" used to result in
"duplicate ... address and port pair" after 4f9b72a229c1.

Fix is to explicitly filter out duplicate addresses returned during
resolution of a name.

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=14969