Remove some #ifdefs and update documentation

Remove some #ifdefs and update documentation

* doc/lispref/processes.texi (Network Processes): Remove
mention of `dns'.

* lisp/net/network-stream.el (open-network-stream): Remove
mention of `dns'.

* src/process.c (Fset_process_filter)
(Fset_process_window_size, Fprocess_contact)
(Fprocess_datagram_address, Fset_process_datagram_address)
(Fset_network_process_option, Fprocess_send_region)
(Fprocess_send_string, Fset_process_coding_system)
(Fset_process_filter_multibyte): Remove the #ifdef
HAVE_GETADDRINFO_A checks.
(Fprocess_send_string): Wait for TLS negotiation.
(wait_for_tls_negotiation): New function.
(send_process): Remove the TLS boot check.

* src/process.c (Fmake_network_process): Ditto.