Set ERL_EPMD_ADDRESS=127.0.0.1 by default

If an EPMD process is spawned during eturnal startup, let it listen on
localhost only.

This reverts commit 3a65d40, since
issue #11 has been addressed by Erlang/OTP 25.0:

erlang/otp@e8c9e12

Resolves #9.

CHANGELOG.md

@@ -18,6 +18,11 @@ project adheres to [Semantic Versioning][SemVer].
   `ENV` variable or a configuration file).
 
 ### Changed
+- If an [EPMD](https://erlang.org/doc/man/epmd.html) process is spawned during
+  eturnal startup, let it listen on `localhost` only (#9). (Note that our Linux
+  packages and container images are
+  [configured](https://eturnal.net/documentation/#ERL_DIST_PORT) to _not_ start
+  an EPMD process.)
 - Omit the code location from log messages, except when debug logging is
   enabled.
 - Apply other minor logging improvements.

build.config

@@ -8,5 +8,5 @@
 {eturnal_user, "eturnal"}.
 {eturnal_bin_prefix, "/opt/eturnal"}. % Points to: /opt/eturnal/bin/eturnal
 {eturnal_etc_prefix, ""}.             % Points to: /etc/eturnal.yml
-{erl_epmd_address, ""}.
+{erl_epmd_address, "127.0.0.1"}.
 {erl_dist_port, ""}.

config/eturnal.service

@@ -21,7 +21,6 @@ LogsDirectory=eturnal
 ProtectSystem=full
 NoNewPrivileges=true
 AmbientCapabilities=CAP_NET_BIND_SERVICE
-#Environment="ERL_EPMD_ADDRESS=127.0.0.1"
 
 [Install]
 WantedBy=multi-user.target

doc/overview.edoc

@@ -540,14 +540,12 @@ feature requires at least Erlang/OTP 23.1 and Rebar3 3.18.0.</em>
 === ERL_EPMD_ADDRESS ===
 
 On eturnal startup, an Erlang Port Mapper Daemon (EPMD) service is spawned (if
-it's not running already and {@section ERL_DIST_PORT} isn't specified). By
-default, this service listens on all available interfaces. Setting the
-`ERL_EPMD_ADDRESS' environment variable tells EPMD to listen on the specified
-comma-seperated list of IP addresses instead. Note that the IPv4 and IPv6
-loopback addresses are implicitly added to this list if not specified. It's
-usually recommended to set `ERL_EPMD_ADDRESS' to `127.0.0.1' (e.g., by calling
-`systemctl edit eturnal' and adding the following line to the `[Service]'
-section: `Environment="ERL_EPMD_ADDRESS=127.0.0.1"').
+it's not running already, and {@section ERL_DIST_PORT} isn't specified). By
+default, eturnal lets EPMD listen on `localhost'. Setting the `ERL_EPMD_ADDRESS'
+environment variable tells EPMD to listen on the specified comma-seperated list
+of IP addresses instead. Note that the IPv4 and IPv6 loopback addresses are
+implicitly added to this list if not specified. Setting `ERL_EPMD_ADDRESS' to an
+empty value lets EPMD listen on all interfaces.
 
 === ERL_EPMD_PORT ===