nixos/coturn: restore logging functionality (#369828)

    ${lib.optionalString (cfg.cert != null) "cert=${cfg.cert}"}

    ${lib.optionalString (cfg.pkey != null) "pkey=${cfg.pkey}"}

    ${lib.optionalString (cfg.dh-file != null) "dh-file=${cfg.dh-file}"}

    no-stdout-log

    syslog

    pidfile=${pidfile}

    ${lib.optionalString cfg.secure-stun "secure-stun"}

    ${lib.optionalString cfg.no-cli "no-cli"}