net: tso: inline tso_count_descs()

tso_count_descs() is a small function doing simple calculation,
and tso_count_descs() is used in fast path, so inline it to
reduce the overhead of calls.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Link: https://lore.kernel.org/r/20221212032426.16050-1-linyunsheng@huawei.com


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