tipc: info leak in __tipc_nl_add_udp_addr()

We should clear out the padding and unused struct members so that we
don't expose stack information to userspace.

Fixes: fdb3accc ('tipc: add the ability to get UDP options via netlink')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>