net/i40e: fix memset size

net/i40e: fix memset size

This causes build error with gcc 7.1.1 :

...dpdk/drivers/net/i40e/i40e_flow.c:2357:2:
error: ‘memset’ used with length equal to number of elements without
       multiplication by element size [-Werror=memset-elt-size]
  memset(off_arr, 0, I40E_MAX_FLXPLD_FIED);
  ^~~~~~

...dpdk/drivers/net/i40e/i40e_flow.c:2358:2:
error: ‘memset’ used with length equal to number of elements without
       multiplication by element size [-Werror=memset-elt-size]
  memset(len_arr, 0, I40E_MAX_FLXPLD_FIED);
  ^~~~~~

Fixed by providing correct size to memset.

Fixes: 6ced3dd72f5f ("net/i40e: support flexible payload parsing for FDIR")

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Beilei Xing <beilei.xing@intel.com>