tests/netlink: Assert the route scope of interface's addresses

While here, add one additional IPv4 link-local address to test_46_nofilter
to cover the IPv4 RT_SCOPE_LINK case.

Reviewed by: melifaro, network
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D49226

(cherry picked from commit 5d8b48487acc8375675f2b7c4507c98ac5d0bf75)
(cherry picked from commit e84a17db1cc034b87df7660dadb709a019140c3c)