[dhcp_relay] complete the dhcp_relay service dependency towards teamd (#1356)

This change makes sure that the dhcp_relay service will be started
after teamd service is started from a stopped state.

Author: yxieca

files/build_templates/dhcp_relay.service.j2

@@ -1,7 +1,7 @@
 [Unit]
 Description=DHCP relay container
 Requires=docker.service teamd.service
-After=swss.service
+After=swss.service teamd.service
 
 [Service]
 User={{ sonicadmin_user }}
@@ -10,4 +10,4 @@ ExecStart=/usr/bin/{{ docker_container_name }}.sh attach
 ExecStop=/usr/bin/{{ docker_container_name }}.sh stop
 
 [Install]
-WantedBy=multi-user.target
+WantedBy=multi-user.target teamd.service