rsyslog: fix config file comment style

The upstream versions of rsyslog (v8 and higher) have this commit to fix
the config file comment issue. Carry this patch here until the version
is bumped.

Signed-off-by: Matthew Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Clayton Shotwell <clayton.shotwell@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>