tc-testing: add a test case for ETS offload

tc-testing: add a test case for ETS offload

While reviewing the fix for unintentional u32 overflows in ets offload
code, Jamal said:

 [...]

 > otherwise a tdc test should cover it fine (when you get to the
 > netdevsim change perhaps)

Extend tdc to allow setting hw-tc-offload via ethtool, and
add a test case to reproduce the division by zero fixed in [1].

[1] https://lore.kernel.org/all/CAM0EoMm17wsYZmdFLshH3_-GrZtzd=i0xnoO2yiVB=-N4761mw@mail.gmail.com/

Suggested-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Co-developed-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Link: https://patch.msgid.link/39129c374cbd00147b8c5afc04db59db62b50acc.1773945414.git.dcaratti@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>