batman-adv: fix coccinelle warnings

net/batman-adv/network-coding.c:1535:1-7: Replace memcpy with struct assignment

Generated by: coccinelle/misc/memcpy-assign.cocci
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Martin Hundebøll <martin@hundeboll.net>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>