graph/db: update test opaque addr to be valid

The first byte of an opaque addr must be one that we dont understand
yet. We do this update in preparation for doing an on-the-fly parse of
persisted opaque addrs to see if they contain addrs that we now support.
For this to work, the first byte cant be 0x01 since this maps to a known
address.

graph/db/graph_test.go

@@ -39,7 +39,10 @@ var (
 		"[2001:db8:85a3:0:0:8a2e:370:7334]:80")
 	testAddrs      = []net.Addr{testAddr, anotherAddr}
 	testOpaqueAddr = &lnwire.OpaqueAddrs{
-		Payload: []byte{0x01, 0x02, 0x03, 0x04, 0x05, 0x06},
+		// NOTE: the first byte is a protocol level address type. So
+		// for we set it to 0xff to guarantee that we do not know this
+		// type yet.
+		Payload: []byte{0xff, 0x02, 0x03, 0x04, 0x05, 0x06},
 	}
 
 	testRBytes, _ = hex.DecodeString("8ce2bc69281ce27da07e6683571319d18" +