channeldb: Serialize/deserialize AMP struct in hop

The AMP struct in a hop was never being set when deserizlied. Also,
the AMP TLV record was not being added when the hop was serialized.
This sets the TLV record when serializing and correctly sets the
AMP struct on the hop when that record is present.

Co-authored-by: BitcoinCoderBob <90647227+BitcoinCoderBob@users.noreply.github.com>
Co-authored-by: Tee8z <tee8z@protonmail.com>

channeldb/payments_test.go

@@ -44,11 +44,25 @@ var (
 		LegacyPayload:    true,
 	}
 
+	testHop3 = &route.Hop{
+		PubKeyBytes:      route.NewVertex(pub),
+		ChannelID:        12345,
+		OutgoingTimeLock: 111,
+		AmtToForward:     555,
+		CustomRecords: record.CustomSet{
+			65536: []byte{},
+			80001: []byte{},
+		},
+		AMP:      record.NewAMP([32]byte{0x69}, [32]byte{0x42}, 1),
+		Metadata: []byte{1, 2, 3},
+	}
+
 	testRoute = route.Route{
 		TotalTimeLock: 123,
 		TotalAmount:   1234567,
 		SourcePubKey:  vertex,
 		Hops: []*route.Hop{
+			testHop3,
 			testHop2,
 			testHop1,
 		},