route: fix typo

Change-Id: I41d449e071f1d40bdc69288e7290af168b6b0d3c
Reviewed-on: https://go-review.googlesource.com/29693
Reviewed-by: Ian Lance Taylor <iant@golang.org>

route/route_test.go

@@ -325,7 +325,7 @@ func fetchAndParseRIB(af int, typ RIBType) ([]Message, error) {
 	return ms, nil
 }
 
-// propVirtual is a proprietary viertual network interface.
+// propVirtual is a proprietary virtual network interface.
 type propVirtual struct {
 	name         string
 	addr, mask   string