[SPARK-10598] [DOCS]

Comments preceding toMessage method state: "The edge partition is encoded in the lower
   * 30 bytes of the Int, and the position is encoded in the upper 2 bytes of the Int.". References to bytes should be changed to bits.

This contribution is my original work and I license the work to the Spark project under it's open source license.

Author: Robin East <robin.east@xense.co.uk>

Closes #8756 from insidedctm/master.

graphx/src/main/scala/org/apache/spark/graphx/impl/RoutingTablePartition.scala

@@ -34,7 +34,7 @@ object RoutingTablePartition {
   /**
    * A message from an edge partition to a vertex specifying the position in which the edge
    * partition references the vertex (src, dst, or both). The edge partition is encoded in the lower
-   * 30 bytes of the Int, and the position is encoded in the upper 2 bytes of the Int.
+   * 30 bits of the Int, and the position is encoded in the upper 2 bits of the Int.
    */
   type RoutingTableMessage = (VertexId, Int)