dabba: made switch/output name more consistent.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
test: refactor interface offload output testing.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
test: check offload values against ethtool.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>