batman-adv: Adjust name for batadv_dat_send_data

The send functions in batman-adv are expected to consume the skb when
either the data is queued up for the underlying driver or when some
precondition failed. batadv_dat_send_data didn't do this and instead
created a copy of the skb, modified it and queued the copy up for
transmission. The caller has to take care that the skb is handled correctly
(for example free'd) when batadv_dat_send_data returns.

This unclear behavior already lead to memory leaks in the recent past.
Renaming the function to batadv_dat_forward_data should make it easier to
identify that the data is forwarded but the skb is not actually
send+consumed.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>