Add qos_* iptables chain namespace for QoS

Prefix the names of the iptables chains used for QoS with "qos_" to
allow for identification of QoS chains for removal across configuration
changes.  When clearing QoS iptables chains, only remove chains with the
namespace prefix in order to preserve user and/or other package chains
in the mangle table.

Signed-off-by: Kevin Locke <klocke@digitalenginesoftware.com>

SVN-Revision: 28622