i40e/base: future proof some sizeof calls

i40e/base: future proof some sizeof calls

Make sure the sizeof() calls are taking the size of the actual
struct that we care about. By using the pointer variable, it will
always get the right struct size, even if the variable type
changes sometime in the future.

Test report: http://www.dpdk.org/ml/archives/dev/2015-May/017384.html

Signed-off-by: Helin Zhang <helin.zhang@intel.com>
Acked-by: Jijiang Liu <jijiang.liu@intel.com>
Tested-by: Min Cao <min.cao@intel.com>