acm/distrib/plugin: fix config file comments

[sm pr]db_dump_dir commented out is changed from:

	# [sm pr]db_dump_dir (null)

to:

	# [sm pr]db_dump_dir /etc/rdma/[sm pr]db_dump

Signed-off-by: Ilya Nelkenbaum <ilyan@mellanox.com>
Signed-off-by: Hal Rosenstock <hal@mellanox.com>