Please provide "fixed in version" information, in order us to start testing this bug.

Sorry, I specified the wrong package for fixed in version (it isn't a neutron issue, but a puppet/OSP-d one). I've updated the package to the relevant puppet module package where the default is set. I'm not 100% certain this is correct, because while the puppet modules is what has changed, verification entails ensuring that the heat templates used in a default OSP-d deployment do not alter the default values set by the puppet modules.

verified :
/etc/neutron/dhcp_agent.ini:# dhcp_delete_namespaces = True
/etc/neutron/l3_agent.ini:# router_delete_namespaces = True
[root@overcloud-controller-0 - ~]# rpm -qa |grep neutron
openstack-neutron-7.0.1-8.el7ost.noarch
python-neutron-7.0.1-8.el7ost.noarch
openstack-neutron-common-7.0.1-8.el7ost.noarch
python-neutron-lbaas-7.0.0-2.el7ost.noarch
openstack-neutron-openvswitch-7.0.1-8.el7ost.noarch
openstack-neutron-ml2-7.0.1-8.el7ost.noarch
python-neutronclient-3.1.0-1.el7ost.noarch

[stack@instack yum.repos.d]$ rpm -qa |grep -i triple
openstack-tripleo-0.0.7-1.el7ost.noarch
openstack-tripleo-heat-templates-0.8.7-2.el7ost.noarch
openstack-tripleo-puppet-elements-0.0.2-1.el7ost.noarch
python-tripleoclient-0.0.11-5.el7ost.noarch
openstack-tripleo-common-0.0.2-4.el7ost.noarch
openstack-tripleo-image-elements-0.9.7-1.el7ost.noarch

[heat-admin@overcloud-controller-0 ~]$ rpm -qa |grep openstack-puppet-modules
openstack-puppet-modules-7.0.3-1.el7ost.noarch

created dhcp & router namespace and when delete router & network the namespaces deleted automatically

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHEA-2016-0604.html