MFC r349284: Make ELEMENT INDEX validation more strict.

MFC r349284: Make ELEMENT INDEX validation more strict.

SES specifications tell: "The Additional Element Status descriptors shall
be in the same order as the status elements in the Enclosure Status
diagnostic page".  It allows us to question ELEMENT INDEX that is lower
then values we already processed.  There are many SAS2 enclosures with
this kind of problem.

While there, add more specific error messages for cases when ELEMENT INDEX
is obviously wrong.  Also skip elements with INVALID bit set.