qmp: Simplify recognition of capability negotiation command

Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

monitor.c

@@ -4783,9 +4783,9 @@ static int monitor_can_read(void *opaque)
     return (mon->suspend_cnt == 0) ? 1 : 0;
 }
 
-static int invalid_qmp_mode(const Monitor *mon, const char *cmd_name)
+static int invalid_qmp_mode(const Monitor *mon, const mon_cmd_t *cmd)
 {
-    int is_cap = compare_cmd(cmd_name, "qmp_capabilities");
+    int is_cap = cmd->mhandler.cmd_new == do_qmp_capabilities;
     return (qmp_cmd_mode(mon) ? is_cap : !is_cap);
 }
 
@@ -5079,13 +5079,8 @@ static void handle_qmp_command(JSONMessageParser *parser, QList *tokens)
 
     cmd_name = qdict_get_str(input, "execute");
     trace_handle_qmp_command(mon, cmd_name);
-    if (invalid_qmp_mode(mon, cmd_name)) {
-        qerror_report(QERR_COMMAND_NOT_FOUND, cmd_name);
-        goto err_out;
-    }
-
     cmd = qmp_find_cmd(cmd_name);
-    if (!cmd) {
+    if (!cmd || invalid_qmp_mode(mon, cmd)) {
         qerror_report(QERR_COMMAND_NOT_FOUND, cmd_name);
         goto err_out;
     }