Updated example plugin to behave the same for IPv4 as IPv6

This patch updates the example plugin to behave the same for IPv4
as it does for IPv6.

Signed-off-by: Pete Birley <pete@port.direct>

plugins/example/plugin.go

@@ -91,8 +91,9 @@ func exampleHandler6(req, resp dhcpv6.DHCPv6) (dhcpv6.DHCPv6, bool) {
 // exampleHandler4 behaves like exampleHandler6, but for DHCPv4 packets. It
 // implements the `handler.Handler4` interface.
 func exampleHandler4(req, resp *dhcpv4.DHCPv4) (*dhcpv4.DHCPv4, bool) {
-	// TODO check the MAC address in the request
-	//      if it is present in StaticRecords, forge a response
-	//      and stop processing.
-	return resp, true
+	log.Printf("plugins/example: received DHCPv4 packet: %s", req.Summary())
+	// return the unmodified response, and false. This means that the next
+	// plugin in the chain will be called, and the unmodified response packet
+	// will be used as its input.
+	return resp, false
 }