system-offloads-traffic.at: Fix requesting HW offloaded flows from veth.

system-offloads-traffic.at: Fix requesting HW offloaded flows from veth.

veth pair doesn't offload anything to HW. i.e. we should use 'tc' type
while requesting flows. 'offloaded' kept just in case to not update the
test if veths will be HW offloaded someday.

Additionally fixed missed for unknown reason 'ipv4' fields. Also
dropped stripping of the errors from log.

Fixes test:

  2: offloads - ping between two ports - offloads enabled ok

CC: Gavi Teitz <gavi@mellanox.com>
Fixes: d63ca5329ff9 ("dpctl: Properly reflect a rule's offloaded to HW state")
Acked-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>