Panic when server initiated disconnect happens at the same time as client transaction

Observed in https://github.com/ovn-kubernetes/ovn-kubernetes/pull/5897

16  0x0000000000479692 in runtime.gopanic
    at /usr/local/go/src/runtime/panic.go:792
17  0x000000000041105e in runtime.chansend
    at /usr/local/go/src/runtime/chan.go:226
18  0x000000000041235a in runtime.selectnbsend
    at /usr/local/go/src/runtime/chan.go:782
19  0x0000000001b55c26 in github.com/ovn-kubernetes/libovsdb/client.(*ovsdbClient).transact
    at /workspace/ovn-kubernetes/go-controller/vendor/github.com/ovn-kubernetes/libovsdb/client/client.go:844
20  0x0000000001b55165 in github.com/ovn-kubernetes/libovsdb/client.(*ovsdbClient).Transact
    at /workspace/ovn-kubernetes/go-controller/vendor/github.com/ovn-kubernetes/libovsdb/client/client.go:809
21  0x0000000001eec9eb in github.com/ovn-org/ovn-kubernetes/go-controller/pkg/libovsdb/ops.TransactWithRetry.func1
    at /workspace/ovn-kubernetes/go-controller/pkg/libovsdb/ops/transact.go:25
22  0x00000000008f4102 in k8s.io/apimachinery/pkg/util/wait.loopConditionUntilContext.func1
    at /workspace/ovn-kubernetes/go-controller/vendor/k8s.io/apimachinery/pkg/util/wait/loop.go:53
23  0x00000000008f3cd5 in k8s.io/apimachinery/pkg/util/wait.loopConditionUntilContext
    at /workspace/ovn-kubernetes/go-controller/vendor/k8s.io/apimachinery/pkg/util/wait/loop.go:54
24  0x00000000008f4296 in k8s.io/apimachinery/pkg/util/wait.PollUntilContextCancel
    at /workspace/ovn-kubernetes/go-controller/vendor/k8s.io/apimachinery/pkg/util/wait/poll.go:33
25  0x0000000001eec905 in github.com/ovn-org/ovn-kubernetes/go-controller/pkg/libovsdb/ops.TransactWithRetry
    at /workspace/ovn-kubernetes/go-controller/pkg/libovsdb/ops/transact.go:23
26  0x0000000001eecd46 in github.com/ovn-org/ovn-kubernetes/go-controller/pkg/libovsdb/ops.TransactAndCheck
    at /workspace/ovn-kubernetes/go-controller/pkg/libovsdb/ops/transact.go:48
27  0x0000000001eed1db in github.com/ovn-org/ovn-kubernetes/go-controller/pkg/libovsdb/ops.TransactAndCheckAndSetUUIDs
    at /workspace/ovn-kubernetes/go-controller/pkg/libovsdb/ops/transact.go:66
28  0x0000000002115b10 in github.com/ovn-org/ovn-kubernetes/go-controller/pkg/ovn/controller/services.EnsureLBs
    at /workspace/ovn-kubernetes/go-controller/pkg/ovn/controller/services/loadbalancer.go:293
29  0x0000000002122d8e in github.com/ovn-org/ovn-kubernetes/go-controller/pkg/ovn/controller/services.(*Controller).syncService
    at /workspace/ovn-kubernetes/go-controller/pkg/ovn/controller/services/services_controller.go:503
30  0x0000000002120210 in github.com/ovn-org/ovn-kubernetes/go-controller/pkg/ovn/controller/services.(*Controller).processNextWorkItem
    at /workspace/ovn-kubernetes/go-controller/pkg/ovn/controller/services/services_controller.go:299

The channel is trafficSeen. We probably should drain the channel instead of closing/reopening.