route: remove check for unparsed route message bytes

Under some circumstances, DragonFly BSD appears to put more addresses
in route messages than are indicated in the message header. Remove
the recently-added check for unparsed bytes in a route message to
avoid errors.

Change-Id: Id567e4cd49470970f78dbd2decd682c4c00b27fa
Reviewed-on: https://go-review.googlesource.com/c/net/+/322429
Trust: Damien Neil <dneil@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

route/address.go

@@ -422,11 +422,9 @@ func parseAddrs(attrs uint, fn func(int, []byte) (int, Addr, error), b []byte) (
 			b = b[l:]
 		}
 	}
-	if len(b) > 4 {
-		// If there is more data left over after parsing all addresses
-		// than might be needed for alignment, then we have made a mistake
-		// somewhere.
-		return nil, errInvalidMessage
-	}
+	// The only remaining bytes in b should be alignment.
+	// However, under some circumstances DragonFly BSD appears to put
+	// more addresses in the message than are indicated in the address
+	// bitmask, so don't check for this.
 	return as[:], nil
 }