Use registry.receives decorator in neutron.db.dvr_mac_db
Use registry.receives decorator in neutron.db.dvr_mac_db

Switch to registry.receives decorator in neutron.db.dvr_mac_db.

Change-Id: I7f1426adabe1d97b8df11d561454972354c23b14
Partial-Bug: #1668262

noironetworks/neutron,huntxu/neutron,openstack/neutron,huntxu/neutron,mahak/neutron,openstack/neutron,eayunstack/neutron,openstack/neutron,eayunstack/neutron,noironetworks/neutron,mahak/neutron,mahak/neutron