sctp: adjust some codes in a better order in sctp_sendmsg

sctp_sendmsg_new_asoc and SCTP_ADDR_OVER check is only necessary
when daddr is set, so move them up to if (daddr) statement.

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