[SCTP]: Set chunk->data_accepted only if we are going to accept it.

Currently there is a code path in sctp_eat_data() where it is possible
to set this flag even when we are dropping this chunk.

Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>