sctp: user perfect name for Delayed SACK Timer option

The option name of Delayed SACK Timer should be SCTP_DELAYED_SACK,
not SCTP_DELAYED_ACK.

Left SCTP_DELAYED_ACK be concomitant with SCTP_DELAYED_SACK,
for making compatibility with existing applications.

Reference:
8.1.19. Get or Set Delayed SACK Timer (SCTP_DELAYED_SACK)
（http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-25)

Signed-off-by: Shan Wei <[e-mail]>
Acked-by: Wei Yongjun <[e-mail]>
Acked-by: Vlad Yasevich <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/sctp/user.h

···
 #define SCTP_GET_PEER_ADDR_INFO	15
 #define SCTP_DELAYED_ACK_TIME	16
 #define SCTP_DELAYED_ACK SCTP_DELAYED_ACK_TIME
+#define SCTP_DELAYED_SACK SCTP_DELAYED_ACK_TIME
 #define SCTP_CONTEXT	17
 #define SCTP_FRAGMENT_INTERLEAVE	18
 #define SCTP_PARTIAL_DELIVERY_POINT	19 /* Set/Get partial delivery point */

net/sctp/socket.c

···
 		retval = sctp_setsockopt_peer_addr_params(sk, optval, optlen);
 		break;
 
-	case SCTP_DELAYED_ACK:
+	case SCTP_DELAYED_SACK:
 		retval = sctp_setsockopt_delayed_ack(sk, optval, optlen);
 		break;
 	case SCTP_PARTIAL_DELIVERY_POINT:
···
 		retval = sctp_getsockopt_peer_addr_params(sk, len, optval,
 							  optlen);
 		break;
-	case SCTP_DELAYED_ACK:
+	case SCTP_DELAYED_SACK:
 		retval = sctp_getsockopt_delayed_ack(sk, len, optval,
 							  optlen);
 		break;