Description
Prior to the per vlan dhcp relay support was added via 1d16a37 , DhcpResources tag was used to specify the Dhcp relay server information, and all routed interfaces, VLAN interfaces and Port-Channel interfaces were added to listening interfaces for the dhcrelay command in the j2 template.

After the commit with the new DhcpRelay tag, only the dhcp relay vlan, routed interfaces and Port-Channel interfaces are added to the dhcrelay command, but if the dhcp server sits behind a different vlan, the dhcp offer is not getting forwarded.

Steps to reproduce the issue:

1. Configure per vlan dhcp relay
2. Have a dhcp server connected to a VLAN interface in the topology
3. Have dhcp relay configured on another VLAN interface.

Describe the results you received:
DHCP request is getting forwarded to the dhcp server, but DHCP offer received from the server is dropped since it is not in the dhcrelay listening interfaces.

Describe the results you expected:
DHCP offer should be forwarded properly in the case of dhcp server connected to vlan interface.

Additional information you deem important (e.g. issue happens only occasionally):
Manually modified docker-dhcp-relay.supervisord.conf to include the dhcp server VLAN, and dhcp relay is working properly.