SCTP: IPv4 mapped addr not returned in SCTPv6 accept()

An accept() call on a SCTPv6 socket that returns due to connection of
a IPv4 mapped peer will fill out the 'struct sockaddr' with a zero
IPv6 address instead of the IPv4 mapped address of the peer.

This is due to the v4mapped flag not getting copied into the new
socket on accept() as well as a missing check for INET6 socket type in
sctp_v4_to_sk_*addr().

Signed-off-by: Dave Johnson <djohnson@sw.starentnetworks.com>
Cc: Srinivas Akkipeddi <sakkiped@starentnetworks.com>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>