qmp qemu-ga: Fix qemu-ga not to accept "control"

Commit cf869d5317 "qmp: support out-of-band (oob) execution"
accidentally made qemu-ga accept and ignore "control".  Fix that.

Out-of-band execution in a monitor that doesn't support it now fails
with

    {"error": {"class": "GenericError", "desc": "QMP input member 'control' is unexpected"}}

instead of

    {"error": {"class": "GenericError", "desc": "Please enable out-of-band first for the session during capabilities negotiation"}}

The old description is suboptimal when out-of-band cannot not be
enabled, or the command doesn't support out-of-band execution.

The new description is a bit unspecific, but it'll do.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180703085358.13941-12-armbru@redhat.com>

qga/main.c

@@ -586,7 +586,7 @@ static void process_command(GAState *s, QDict *req)
 
     g_assert(req);
     g_debug("processing command");
-    rsp = qmp_dispatch(&ga_commands, QOBJECT(req));
+    rsp = qmp_dispatch(&ga_commands, QOBJECT(req), false);
     if (rsp) {
         ret = send_response(s, rsp);
         if (ret < 0) {