sctp: fix auth_hmacs field's length of struct sctp_cookie

auth_hmacs field of struct sctp_cookie is used for store
Requested HMAC Algorithm Parameter, and each HMAC Identifier
is 2 bytes, so the length should be:
  SCTP_AUTH_NUM_HMACS * sizeof(__u16) + 2
Signed-off-by: NWei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/sctp/structs.h

@@ -422,7 +422,7 @@ struct sctp_cookie {
 	__u32 adaptation_ind;
 
 	__u8 auth_random[sizeof(sctp_paramhdr_t) + SCTP_AUTH_RANDOM_LENGTH];
-	__u8 auth_hmacs[SCTP_AUTH_NUM_HMACS + 2];
+	__u8 auth_hmacs[SCTP_AUTH_NUM_HMACS * sizeof(__u16) + 2];
 	__u8 auth_chunks[sizeof(sctp_paramhdr_t) + SCTP_AUTH_MAX_CHUNKS];
 
 	/* This is a shim for my peer's INIT packet, followed by