[Why]
In commit c903397171, the variable was
renamed from `ERLANG_LIB` to `_ERLANG_LIB`. However the rc.d script was
not updated to reflect that change.
Therefore the script didn't use the expected version of Erlang. This
meant that it could use `lang/erlang` if it was installed (which could
be incompatible) or not start at all.
[How]
The rc.d script is simply updated to use the new variable name. The port
revision is bumped to note the change.
PR: 271269
Reported by: Miroslav Lachman <000.fbsd@quip.cz>