sctp: fix ignoring asoc_id for tcp-style sockets on SCTP_CONTEXT sockopt

A similar fix as Patch "sctp: fix ignoring asoc_id for tcp-style sockets on
SCTP_DEFAULT_SEND_PARAM sockopt" on SCTP_CONTEXT sockopt.

Fixes: 49b037ac ("sctp: use SCTP_FUTURE_ASSOC and add SCTP_CURRENT_ASSOC for SCTP_CONTEXT sockopt")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>