tg3: Increment tx_dropped in tg3_tso_bug()

tg3_tso_bug() drops a packet if it cannot be segmented for any reason.
The number of discarded frames should be incremented accordingly.

Signed-off-by: Alex Pakhunov <alexey.pakhunov@spacex.com>
Signed-off-by: Vincent Wong <vincent.wong2@spacex.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Link: https://lore.kernel.org/r/20231113182350.37472-2-alexey.pakhunov@spacex.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>