[SCTP]: Correctly set daddr for IPv6 sockets during peeloff

During peeloff of AF_INET6 socket, the inet6_sk(sk)->daddr
wasn't set correctly since the code was assuming IPv4 only.
Now we use a correct call to set the destination address.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Acked-by: Sridhar Samudrala <sri@us.ibm.com>