Staging: batman-adv: Aggregate batman packets directly in skb

All originator messages are send through aggregation buffers. Those
buffers can directly be allocated as skb to reduce the cost of
allocation an extra buffer and copying them to a new allocated skb
directly before it gets send.

Now only the skb must be cloned in case of send_packet_to_if as it gets
called by send_packet for each interface. Non-primary ogms must not
cloned at all because they will only send once and the forward_packet
structure is freed by send_outstanding_bat_packet afterwards.

Reported-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>