Start up mgmtd in docker-sonic-vs

FRR 10.0.1 upgrade (sonic-net#20269) brought in a mgmtd
daemon for FRR. This needs to be started up in docker-sonic-vs as part
of the other daemons in this container.

Signed-off-by: Saikrishna Arcot <[email protected]>

Author: saiarcot895

platform/vs/docker-sonic-vs/start.sh

@@ -160,6 +160,8 @@ supervisorctl start vlanmgrd
 
 supervisorctl start zebra
 
+supervisorctl start mgmtd
+
 supervisorctl start staticd
 
 supervisorctl start buffermgrd