sctp: remove reconf_enable from asoc

asoc's reconf support is actually decided by the 4-shakehand negotiation,
not something that users can set by sockopt. asoc->peer.reconf_capable is
working for this. So remove it from asoc.

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