Fix the hwmp code to handle nodes in a "line" topology.
Fix the hwmp code to handle nodes in a "line" topology.

For example, this particular topology didn't work correctly from all
nodes:

[A] - [B] - [C] - [D]

Submitted by:	Monthadar Al Jaberi <monthadar@gmail.com>
Reviewed by:	bschmidt, adrian

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