module: network: monitor ethernet interfaces

State exposed (tag names):

* name: the interface name ("eth0" etc)
* index: the interface index, "ifindex"
* state: operational state (down, up etc)
* mac: the Ethernet hardware address
* ipv4: the *last* IPv4 address added to the interface
* ipv6: the *last* IPv6 address added to the interface

State we monitor (for changes):

* state
* ipv4 addresses
* ipv6 addresses

modules/network.h

@@ -0,0 +1,6 @@
+#pragma once
+
+#include "../module.h"
+#include "../particle.h"
+
+struct module *module_network(const char *iface, struct particle *label);