[SCTP]: Fix IPv6 address flag setting when doing peel-off/accept.

During accept/peeloff we try to copy the list of bound addresses from
the original endpoint to the new one. However, we forgot to set the flag
to say that IPv6 is allowed on the new endpoint.

Signed-off-by: Vladislav Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>