sctp: free msg->chunks when sctp_primitive_SEND return err

sctp: free msg->chunks when sctp_primitive_SEND return err

Last patch "sctp: do not return the transmit err back to sctp_sendmsg"
made sctp_primitive_SEND return err only when asoc state is unavailable.
In this case, chunks are not enqueued, they have no chance to be freed if
we don't take care of them later.

This Patch is actually to revert commit f05e5943fde1 ("sctp: remove the
unused sctp_datamsg_free()"), commit bb765dde8f3b ("sctp: hold the chunks
only after the chunk is enqueued in outq") and commit 51386cdc898c ("sctp:
only drop the reference on the datamsg after sending a msg"), to use
sctp_datamsg_free to free the chunks of current msg.

Fixes: 51386cdc898c ("sctp: only drop the reference on the datamsg after sending a msg")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>