This patch deletes the flexible-array hmac[] from the structure
sctp_authhdr to avoid some sparse warnings:
  # make C=2 CF="-Wflexible-array-nested" M=./net/sctp/
  net/sctp/auth.c: note: in included file (through include/net/sctp/structs.h, include/net/sctp/sctp.h):
  ./include/linux/sctp.h:735:29: warning: nested flexible array
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
 struct sctp_authhdr {
        __be16 shkey_id;
        __be16 hmac_id;
-       __u8   hmac[];
+       /* __u8   hmac[]; */
 };
 
 struct sctp_auth_chunk {
 
 
        tfm = asoc->ep->auth_hmacs[hmac_id];
 
-       digest = auth->auth_hdr.hmac;
+       digest = (u8 *)(&auth->auth_hdr + 1);
        if (crypto_shash_setkey(tfm, &asoc_key->data[0], asoc_key->len))
                goto free;
 
 
         *  3. Compute the new digest
         *  4. Compare saved and new digests.
         */
-       digest = auth_hdr->hmac;
+       digest = (u8 *)(auth_hdr + 1);
        skb_pull(chunk->skb, sig_len);
 
        save_digest = kmemdup(digest, sig_len, GFP_ATOMIC);