selftests: rtnetlink: add addresses with fixed life time

This exercises kernel code path that deal with addresses that have
a limited lifetime.

Without previous fix, this triggers following crash on net-next:
 BUG: KASAN: null-ptr-deref in check_lifetime+0x403/0x670
 Read of size 8 at addr 0000000000000010 by task kworker [..]

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>