net/thunderx: fix Tx checksum handling

net/thunderx: fix Tx checksum handling

The symbols PKT_TX_TCP_CKSUM and PKT_TX_UDP_CKSUM are not bits on a
bitmask. Set l3_offset always for TX offloads, not just for PKT_TX_IP_CKSUM
being true.

Fixes: 1c421f18e095 ("net/thunderx: add single and multi-segment Tx")

Signed-off-by: Maciej Czekaj <maciej.czekaj@caviumnetworks.com>
Signed-off-by: Kamil Rytarowski <kamil.rytarowski@caviumnetworks.com>
Signed-off-by: Zyta Szpak <zyta.szpak@semihalf.com>
Signed-off-by: Slawomir Rosek <slawomir.rosek@semihalf.com>
Signed-off-by: Radoslaw Biernacki <rad@semihalf.com>
Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>