net: dl2k: remove variable tx_use

Variable tx_use is just being incremented and it's never used
anywhere else. The variable and the increment are redundant so
remove it.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20221024143501.2163720-1-colin.i.king@gmail.com


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