fix private channel payment issue #2222

Job	Run time
e2e test for 3-nodes-transfer --env test	4m 12s
e2e test for invoice-ops --env test	3m 48s
e2e test for open-use-close-a-channel --env test	4m 27s
e2e test for udt --env test	4m 8s
e2e test for reestablish --env test	4m 3s
e2e test for cross-chain-hub --env test	4m 12s
e2e test for router-pay --env test	5m 11s
e2e test for udt-router-pay --env test	4m 20s
e2e test for watchtower --env test	5m 32s
e2e test for udt --env xudt-test	4m 15s
e2e test for 3-nodes-transfer --env test --env-var HASH_ALGORITHM=sha256	4m 25s
	48m 33s

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