route/addr: fix ID comparison for AF_INET and AF_INET6 addresses

route/addr: fix ID comparison for AF_INET and AF_INET6 addresses

For AF_INET/IPv4 addresses, the ID equality comparison must include
the net-part of the peer address:

    unshare -n
    ip link add T type dummy
    ip link set T up
    ip addr add 192.168.5.10/24 dev T
    ip addr add 192.168.5.10 peer 192.168.6.1/24 dev T
    ip addr add 192.168.5.10 peer 192.168.7.1/24 dev T
    ip addr add 192.168.5.10 peer 192.168.7.2/24 dev T
    # RTNETLINK answers: File exists

    ip addr change 192.168.5.10 peer 192.168.7.2/24 dev T
    ip addr show | grep 192.168.7.
    # inet 192.168.5.10 peer 192.168.7.1/24 scope global T

For AF_INET6/IPv6 addresses, the prefix length of the address
is not part of the ID:

    unshare -n
    ip link add T type dummy
    ip link set T up
    ip addr add 192.168.7.10/24 dev T
    ip addr add 192.168.7.10/23 dev T
    ip addr add 1:2:3:4:5::1/64 dev T
    ip addr add 1:2:3:4:5::1/63 dev T
    # RTNETLINK answers: File exists

    ip addr change 1:2:3:4:5::1/63 dev T
    ip addr show | grep 1:2:3:4:5::1
    # inet6 1:2:3:4:5::1/64 scope global

*sigh*

http://lists.infradead.org/pipermail/libnl/2016-June/002158.html

Signed-off-by: Thomas Haller <thaller@redhat.com>