Previously this set `ctx->ns_fd[*]` to `-EBADF` until commit
fd2a88b1 ("attach: cleanup macros lxc_proc_close_ns_fd",
but there are some code paths where we call this before
later calling `lxc_proc_put_context_info` which would call
this function again with the file descriptors still
unchanged.
Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>