batman-adv: frag: free unfragmentable packet

batman-adv: frag: free unfragmentable packet

The caller of batadv_frag_send_packet() assume that the skb provided to the
function are always consumed. But the pre-check for an empty payload or the
zero fragment size returned an error without any further actions.

A failed pre-check must use the same error handling code as the rest of the
function.

Cc: stable@vger.kernel.org
Fixes: ee75ed88879a ("batman-adv: Fragment and send skbs larger than mtu")
Signed-off-by: Sven Eckelmann <sven@narfation.org>