net/null: set port id in received mbufs
net/null: set port id in received mbufs

Ensure that the port field is set in mbufs received from the null PMD.

Signed-off-by: Sean Harte <e3a85eeecf01a5fb0a1e2b0a6375c11c7431ec38@intel.com>
Acked-by: John McNamara <af31595c36a4239b9676e9b3a777d3e2f15a6c4d@intel.com>
Acked-by: Tetsuya Mukawa <b347a9f5840345582b30d055e1e99ac6ac7bce3c@igel.co.jp>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk