malloc: fix realloc copy size

malloc: fix realloc copy size

In rte_realloc, if the old element has pad and need to allocate a new
memory, the padding size was not deducted, so more data was copied to
new data area.

Fixes: af75078fece3 ("first public release")
Cc: stable@dpdk.org
Signed-off-by: Xueming Li <xuemingl@mellanox.com>
Reviewed-by: Anatoly Burakov <anatoly.burakov@intel.com>