qemu-ga: add guest-network-get-interfaces command

This command returns an array of:

 [ifname, hwaddr, [ipaddr, ipaddr_family, prefix] ]

for each interface in the system.
Currently, only IPv4 and IPv6 are supported.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
diff --git a/qga/commands-win32.c b/qga/commands-win32.c
index b7600ed..eb8d140 100644
--- a/qga/commands-win32.c
+++ b/qga/commands-win32.c
@@ -263,6 +263,12 @@
     error_set(err, QERR_UNSUPPORTED);
 }
 
+GuestNetworkInterfaceList *qmp_guest_network_get_interfaces(Error **err)
+{
+    error_set(err, QERR_UNSUPPORTED);
+    return NULL;
+}
+
 /* register init/cleanup routines for stateful command groups */
 void ga_command_state_init(GAState *s, GACommandState *cs)
 {