smoketest: T5705: use locally connected remote syslog servers

As there has been no route to the configured syslog servers, smoketests produced:

rsyslogd: omfwd: socket 8: error 101 sending via udp: Network is unreachable

Rather use some fake syslog servers from 127.0.0.0/8 which are directly
connected and we do not need to look up a route, which will suppress the above
error message.

(cherry picked from commit 744ecfe60ed3633775feeb3da767a88709fd626c)