sctp: fix to indicate ASCONF support in INIT-ACK only if peer has such capable

This patch fix to indicate ASCONF support in INIT-ACK only if peer has
such capable.

This patch also fix to calc the chunk size if peer has no FWD-TSN
capable.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>