Correcting the cache alignment for Table_cache_instance.

• Size of Table_cache_instance is 224 (64 bits processor)

• To avoid cache sharing padding of cacheline size was added.
  This padding fails to generate closet possible alignment
  and infact causes bloating with size = 352 (128 bytes cacheline)

• Proposed patch ensure that structure is cache aligned.
  (will submit the patch through github).

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With patch a marginal improvement is seen with multi-numa nodes though not significant to classify this as performance issue.