test: update set of tests to supply data for the set of extra bytes

In this commit, we update the tests to always supply data for the extra
bytes within the HopData payload. This ensures that the bytes are
properly encoded/decoded at each hop.

Author: Roasbeef

sphinx_test.go

@@ -7,9 +7,9 @@ import (
 	"reflect"
 	"testing"
 
-	"github.com/davecgh/go-spew/spew"
 	"github.com/btcsuite/btcd/btcec"
 	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/davecgh/go-spew/spew"
 )
 
 // BOLT 4 Test Vectors
@@ -115,6 +115,7 @@ func newTestRoute(numHops int) ([]*Router, *[]HopData, *OnionPacket, error) {
 			OutgoingCltv:  uint32(i),
 		})
 		copy(hopsData[i].NextAddress[:], bytes.Repeat([]byte{byte(i)}, 8))
+		copy(hopsData[i].ExtraBytes[:], bytes.Repeat([]byte{byte(i)}, padSize))
 	}
 
 	// Generate a forwarding message to route to the final node via the