net/thunderx: fix Tx desc corruption in scatter-gather mode

net/thunderx: fix Tx desc corruption in scatter-gather mode

For performance reasons, word1 of send_hdr_s
sub descriptor was not cleared assuming it is always
having default value of zero since it comes from fixed
offsets of SQ buffer.
This is causing issues in case of SG mode because,
the size of send command might change and hence the word1
of send_hdr_s is not always at fixed offsets of the SQ buffer
and hence not having default value of zero.

This fixes the issue by clearing the word1 in case of SG mode
for every packet.

Fixes: 1c421f18e095 ("net/thunderx: add single and multi-segment Tx")
Cc: stable@dpdk.org
Signed-off-by: Subrahmanyam Nilla <snilla@caviumnetworks.com>
Signed-off-by: Nithin Dabilpuram <nithin.dabilpuram@caviumnetworks.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>