net: fix IPv6 checksum with TSO

net: fix IPv6 checksum with TSO

The ol_flags check lacks of flag for IPv6 which causes checksum
flag configuration error while IPv6/TCP TSO packet is sent.
This patch fixes the issue by adding PKT_TX_TCP_SEG flag.

The rte_net_intel_cksum_flags_prepare() function prepares the
pseudo header checksum in packet data when doing checksum or TSO
offload.

Fixes: 520059a41aa9 ("net: check fragmented headers in non-debug as well")

Signed-off-by: Yuying Zhang <yuying.zhang@intel.com>
Tested-by: Xi Zhang <xix.zhang@intel.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>