[VOL-3482] Do not restart DHCP/EAPOL exchanges that are already in progress

Change-Id: Iebf3150e2046e4d124101e70fe237bbfc2daa3ff
diff --git a/internal/bbsim/devices/olt.go b/internal/bbsim/devices/olt.go
index c883e95..9610961 100644
--- a/internal/bbsim/devices/olt.go
+++ b/internal/bbsim/devices/olt.go
@@ -322,6 +322,7 @@
 	// terminate the OLT's processNniPacketIns go routine
 	go o.nniHandle.Close()
 	close(o.nniPktInChannel)
+	o.enableContextCancel()
 
 	time.Sleep(time.Duration(rebootDelay) * time.Second)