batman-adv: frag: fix primary_if leak on failed linearization

batman-adv: frag: fix primary_if leak on failed linearization

If the skb has a frag_list, it must be linearized before it can be split
using skb_split(). But when this step failed, it must not only free the skb
but also take care of the reference to the already found primary_if.

Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Fixes: a063f2fba3fa ("batman-adv: Don't skb_split skbuffs with frag_list")
Signed-off-by: Sven Eckelmann <sven@narfation.org>