xfrm: Skip redundant statistics update for crypto offload

In the crypto offload path, every packet is still processed by the
software stack. The state's statistics required for the expiration
check are being updated in software.

However, the code also calls xfrm_dev_state_update_stats(), which
triggers a query to the hardware device to fetch statistics. This
hardware query is redundant and introduces unnecessary performance
overhead.

Skip this call when it's crypto offload (not packet offload) to avoid
the unnecessary hardware access, thereby improving performance.

Signed-off-by: Jianbo Liu <jianbol@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>