[SCTP] Fix leak in sctp_getsockopt_local_addrs when copy_to_user fails

If the copy_to_user or copy_user calls fail in sctp_getsockopt_local_addrs(),
the function should free locally allocated storage before returning error.
Spotted by Coverity.

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