[WIP] Add support for ipv4.dhcp.ranges

As long as discussed here [1], OVN has a configuration to exclude IPs from DHCP
pool and it was not supported yet. So using 'ipv4.dhcp.ranges', we get
reserverd IPs using negative logic for provided subnet

[1]: `https://discuss.linuxcontainers.org/t/ovn-dhcp-ranges/21290/3`i

Signed-off-by: Winicius Silva <winiciusab12@gmail.com>

internal/server/network/driver_ovn.go

@@ -360,7 +360,8 @@ func (n *ovn) Validate(config map[string]string) error {
 
 			return validate.IsNetworkAddressCIDRV4(value)
 		}),
-		"ipv4.dhcp": validate.Optional(validate.IsBool),
+		"ipv4.dhcp":        validate.Optional(validate.IsBool),
+		"ipv4.dhcp.ranges": validate.Optional(validate.IsListOf(validate.IsNetworkRangeV4)),
 		"ipv6.address": validate.Optional(func(value string) error {
 			if validate.IsOneOf("none", "auto")(value) == nil {
 				return nil
@@ -1971,6 +1972,12 @@ func (n *ovn) getDHCPv4Reservations() ([]iprange.Range, error) {
 		return nil, err
 	}
 
+	allowedNets := []*net.IPNet{n.DHCPv4Subnet()}
+	dhcpRanges, err := parseIPRange(n.config["ipv4.dhcp.ranges"], allowedNets...)
+	if err != nil {
+		return nil, err
+	}
+
 	return dhcpReserveIPv4s, nil
 }