ethdev: fix comments of packet integrity flow item

ethdev: fix comments of packet integrity flow item

The Doxygen comments are placed before the related lines,
but the markers were /**< instead of /**

The struct rte_flow_item_integrity did not appear in Doxygen output
because there was no general comment for the struct.

Fixes: b10a421a1f3b ("ethdev: add packet integrity check flow rules")

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Acked-by: Ajit Khaparde <ajit.khaparde@broadcom.com>