gve: Secure enough bytes in the first TX desc for all TCP pkts

gve: Secure enough bytes in the first TX desc for all TCP pkts

[ Upstream commit 3ce9345580974863c060fa32971537996a7b2d57 ]

Non-GSO TCP packets whose SKBs' linear portion did not include the
entire TCP header were not populating the first Tx descriptor with
as many bytes as the vNIC expected. This change ensures that all
TCP packets populate the first descriptor with the correct number of
bytes.

Fixes: 893ce44df565 ("gve: Add basic driver framework for Compute Engine Virtual NIC")
Signed-off-by: Shailend Chand <shailend@google.com>
Link: https://lore.kernel.org/r/20230403172809.2939306-1-shailend@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>