sctp: use SCTP_FUTURE_ASSOC for SCTP_LOCAL_AUTH_CHUNKS sockopt

Check with SCTP_FUTURE_ASSOC instead in
sctp_getsockopt_local_auth_chunks, it's compatible with 0.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>