[logrotate]Fix logrotate firstaction script to reflect correct size (s…

…onic-net#12599)

- Why I did it
Fix logrotate firstaction script to reflect correct size. The size was modified to change dynamically based on disk size. However this variable was not updated
sonic-net#9504

- How I did it
Updated the variable based on disk size

- How to verify it
Verify in the generated rsyslog file if the variable is correctly generated from jinja template

files/image_config/logrotate/rsyslog.j2

@@ -50,7 +50,11 @@
         NUM_LOGS_TO_ROTATE=8
 
         # Adjust LOG_FILE_ROTATE_SIZE_KB to reflect the "size" parameter specified above, in kB
+{% if var_log_kb <= 204800 %}
         LOG_FILE_ROTATE_SIZE_KB=1024
+{% else %}
+        LOG_FILE_ROTATE_SIZE_KB=16384
+{% endif %}
 
         # Reserve space for btmp, wtmp, dpkg.log, monit.log, etc., as well as logs that
         # should be disabled, just in case they get created and rotated