doc: fix brick port ranges in admin guide.

Change-Id: Ie6ac43ea435b7b21ac2b7975cbfe38126b170100
BUG: 1095595
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/7855
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Niels de Vos <ndevos@redhat.com>