sockets: Convert to new qapi union layout

We have two issues with our qapi union layout:
1) Even though the QMP wire format spells the tag 'type', the
C code spells it 'kind', requiring some hacks in the generator.
2) The C struct uses an anonymous union, which places all tag
values in the same namespace as all non-variant members. This
leads to spurious collisions if a tag value matches a non-variant
member's name.

Make the conversion to the new layout for socket-related code.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1445898903-12082-17-git-send-email-eblake@redhat.com>
[Commit message tweaked slightly]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
diff --git a/qemu-nbd.c b/qemu-nbd.c
index 422a607..3afec76 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -362,17 +362,17 @@
 
     saddr = g_new0(SocketAddress, 1);
     if (sockpath) {
-        saddr->kind = SOCKET_ADDRESS_KIND_UNIX;
-        saddr->q_unix = g_new0(UnixSocketAddress, 1);
-        saddr->q_unix->path = g_strdup(sockpath);
+        saddr->type = SOCKET_ADDRESS_KIND_UNIX;
+        saddr->u.q_unix = g_new0(UnixSocketAddress, 1);
+        saddr->u.q_unix->path = g_strdup(sockpath);
     } else {
-        saddr->kind = SOCKET_ADDRESS_KIND_INET;
-        saddr->inet = g_new0(InetSocketAddress, 1);
-        saddr->inet->host = g_strdup(bindto);
+        saddr->type = SOCKET_ADDRESS_KIND_INET;
+        saddr->u.inet = g_new0(InetSocketAddress, 1);
+        saddr->u.inet->host = g_strdup(bindto);
         if (port) {
-            saddr->inet->port = g_strdup(port);
+            saddr->u.inet->port = g_strdup(port);
         } else  {
-            saddr->inet->port = g_strdup_printf("%d", NBD_DEFAULT_PORT);
+            saddr->u.inet->port = g_strdup_printf("%d", NBD_DEFAULT_PORT);
         }
     }