plugins: Fix two resource leaks in setup_socket()

Either accept() fails or exits normally, we need to close the fd.

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Alex Chen <alex.chen@huawei.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20201109082829.87496-3-alex.chen@huawei.com>
Message-Id: <20201110192316.26397-3-alex.bennee@linaro.org>

contrib/plugins/lockstep.c

@@ -268,11 +268,13 @@ static bool setup_socket(const char *path)
     socket_fd = accept(fd, NULL, NULL);
     if (socket_fd < 0 && errno != EINTR) {
         perror("accept socket");
+        close(fd);
         return false;
     }
 
     qemu_plugin_outs("setup_socket::ready\n");
 
+    close(fd);
     return true;
 }