It's a somewhat documented (and sometimes crucial indeed) option:

$ cat /etc/sysconfig/syslogd
# Options to syslogd
# -m 0  Disables 'MARK' messages.
# -r    Enables logging from remote machines.
# -x    Disables DNS lookups on messages recieved with -r.
#
# See syslogd(8) for more details.
SYSLOGD_OPTIONS='-u syslogd -j /var/resolv -r -x'

# service syslogd reload
Stopping system logger service:  [ DONE ]
Starting system logger service: /sbin/syslogd: invalid option -- x
usage: syslogd [-drvh] [-l hostlist] [-m markinterval] [-n] [-p path]
 [-s domainlist] [-f conffile] [-i IP address] [-u username]
 [FAILED]

Was it a 3rd party patch (with corresponding sysconfig file modification) but being async-dropped afterwards?

...or is sysconfig stuff rsyslogd-related?..

Пакет был удалён в августе прошлого года:
http://git.altlinux.org/tasks/archive/done/_207/211999/