ganglia: fix config for lucid hosts

Commit Idfed68 (Set SO_RCVBUF on gmond listeners to a sensible value)
introduced a "buffer" option, which looks like it's unsupported on the
lucid version of Ganglia.

Adjust the template to make it dependent on lsbdistrelease -- it's ugly,
but it should do it.

Change-Id: Icc537650550af9d05da473d42df2fd83851a7fff