sctp: clean up __sctp_connect

__sctp_connect is doing quit similar things as sctp_sendmsg_new_asoc.
To factor out common functions, this patch is to clean up their code
to make them look more similar:

  1. create the asoc and add a peer with the 1st addr.
  2. add peers with the other addrs into this asoc one by one.

while at it, also remove the unused 'addrcnt'.

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