app/testpmd: fix L4 checksum in multi-segments

app/testpmd: fix L4 checksum in multi-segments

Testpmd forwards packets in checksum mode that it needs to calculate
the checksum of each layer's protocol.

In process_inner_cksums, when parsing tunnel packets, inner L4 offset
should be outer_l2_len + outer_l3_len + l2_len + l3_len.

In process_outer_cksums, when parsing tunnel packets, outer L4 offset
should be outer_l2_len + outer_l3_len.

Fixes: e6b9d6411e91 ("app/testpmd: add SW L4 checksum in multi-segments")
Cc: stable@dpdk.org
Signed-off-by: Kevin Liu <kevinx.liu@intel.com>
Acked-by: Yuying Zhang <yuying.zhang@intel.com>
Acked-by: Aman Singh <aman.deep.singh@intel.com>