virtio_net: extract interrupt coalescing settings to a structure

Extract interrupt coalescing settings to a structure so that it could be
reused in other data structures.

Signed-off-by: Gavin Li <gavinl@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Heng Qi <hengqi@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230731070656.96411-2-gavinl@nvidia.com


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