Not strictly part of the ticket, but added because the first tests I
did with the existing code returned NSAS_INVALID_RESPONSE messages. This
was a common error to three conditions: the change separates these
out and logs a different message for each one.  It also changes the
severity of two of those conditions (which are caused by the contents
of the returned packet) from ERROR to DEBUG.

(Of course, once the change was made, the original problem could not
be reproduced...
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