client.Update does not prune immutable fields

[dave-tucker]

// update many fields
bridgeRow.UUID = uuid
bridgeRow.ExternalIds["baz"] = "foobar"
bridgeRow.OtherConfig = map[string]string{"foo": "bar"}
ops, err = suite.client.Where(bridgeRow).Update(bridgeRow)
require.NoError(suite.T(), err)
reply, err = suite.client.Transact(ops...)
require.NoError(suite.T(), err)
opErrs, err := ovsdb.CheckOperationResults(reply, ops)
require.NoErrorf(suite.T(), err, "%+v", opErrs)

Fails with an error:

=== RUN   TestOVSIntegrationTestSuite/TestUpdate
    ovs_integration_test.go:507: 
                Error Trace:    ovs_integration_test.go:507
                Error:          Received unexpected error:
                                1 ovsdb operations failed
                Test:           TestOVSIntegrationTestSuite/TestUpdate
                Messages:       [constraint violation: Cannot update immutable column name in table Bridge.]

The immutable fields should be removed before from the ovsdb.Row before it's sent to the server