idpf: make virtchnl2.h self-contained

To ease maintaining of virtchnl2.h, which already is messy enough,
make it self-contained by adding missing if_ether.h include due to
%ETH_ALEN usage.
At the same time, virtchnl2_lan_desc.h is not used anywhere in the
file, so move this include to idpf_txrx.h to speed up C preprocessing.

Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Link: https://lore.kernel.org/r/20240327142241.1745989-3-aleksander.lobakin@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>