esp4_offload/esp6_offload provide GSO/GRO batching for ESP and are not
autoloaded when an SA is created, costing around a third of the mesh's
encrypted throughput. Load the one matching each secured mesh's
underlay family.
Also document the per-SA single-core limit and pcrypt as an option.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
jackos1998