dhcpv4: rename iface->dhcpv4_local -> iface->dhcpv4_own_ip

dhcpv4: rename iface->dhcpv4_local -> iface->dhcpv4_own_ip

"local" isn't very informative, the local what?

In addition, use a struct odhpd_ipaddr instead of a struct in_addr, the
former can already store the prefix_len, broadcast and netmask address,
this will allow the separate iface->dhcpv4_bcast and iface->dhcpv4_mask
members to be removed (see subsequent patches).

Signed-off-by: David Härdeman <[email protected]>
Link: https://github.com/openwrt/odhcpd/pull/320
Signed-off-by: Álvaro Fernández Rojas <[email protected]>