netlink: Fix getting route scope of interface's IPv4 addresses

sin_addr of a struct sockaddr_in is stored in network byte order, but
IN_LOOPBACK() and IN_LINKLOCAL() want the host order.

Reviewed by: melifaro, network
Fixes: 7e5bf68495cc netlink: add netlink support
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D49226