mlxsw: pci: Do not store SKB for RDQ elements

The previous patch used page pool to allocate buffers for RDQ. With this
change, 'elem_info->u.rdq.skb' is not used anymore, as we do not allocate
SKB before getting the packet, we hold page pointer and build the SKB
around it once packet is received.

Remove the union and store SKB pointer for SDQ only.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/23a531008936dc9a1a298643fb1e4f9a7b8e6eb3.1718709196.git.petrm@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>