net/i40e: fix integer overflow

net/i40e: fix integer overflow

When configuring i40e rx queue, the temporary variable to store max
packet length is not big enough which leads to integer overflow issue.
This patch fixes the issue by removing the variable and using the
expression directly since the variable is only used once.

Fixes: 4861cde46116 ("i40e: new poll mode driver")
Cc: stable@dpdk.org
Signed-off-by: Xiao Zhang <xiao.zhang@intel.com>
Reviewed-by: Xiaolong Ye <xiaolong.ye@intel.com>