batman-adv: fix batadv_forw_packet kerneldoc for list attribute

The forw_packet list node is wrongly attributed to the icmp socket code.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>