selftests: drv-net: update remaining Python init files

Convert remaining __init__ files similar to what we did in
commit b615879d ("selftests: drv-net: make linters happy with our imports")

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>