pay: Fix final TLV payload if not going through MPP modifiers

Reported-by: ZmnSCPxj
Signed-off-by: Christian Decker <@cdecker>

Changelog-Fixed: pay: Correct a case where we put the sub-payment value instead of the *total* value in the `total_msat` field of a multi-part payment.

plugins/libplugin-pay.c

@@ -1076,6 +1076,7 @@ static void payment_add_hop_onion_payload(struct payment *p,
 	u32 cltv = p->start_block + next->delay + 1;
 	u64 msat = next->amount.millisatoshis; /* Raw: TLV payload generation*/
 	struct tlv_field **fields;
+	struct payment *root = payment_root(p);
 	static struct short_channel_id all_zero_scid = {.u64 = 0};
 
 	/* This is the information of the node processing this payload, while
@@ -1111,8 +1112,9 @@ static void payment_add_hop_onion_payload(struct payment *p,
 
 		if (payment_secret != NULL) {
 			assert(final);
-			tlvstream_set_tlv_payload_data(fields, payment_secret,
-						       msat);
+			tlvstream_set_tlv_payload_data(
+			    fields, payment_secret,
+			    root->amount.millisatoshis); /* Raw: TLV payload generation*/
 		}
 		break;
 	}

tests/test_pay.py

@@ -3308,7 +3308,6 @@ def test_listpays_ongoing_attempt(node_factory, bitcoind, executor):
     l1.rpc.listpays()
 
 
-@pytest.mark.xfail(strict=True)
 @unittest.skipIf(not DEVELOPER, "needs use_shadow")
 def test_mpp_waitblockheight_routehint_conflict(node_factory, bitcoind, executor):
     '''