[dhcp_relay] make dhcp_relay service depends on teamd as well (#1348)

When teamd service restarted, the port channels will be recreated.

Dhcp relay service needs to be restarted after that to listen on the
right port channels.

files/build_templates/dhcp_relay.service.j2

@@ -1,6 +1,6 @@
 [Unit]
 Description=DHCP relay container
-Requires=docker.service
+Requires=docker.service teamd.service
 After=swss.service
 
 [Service]