In the Linux kernel, the following vulnerability has been resolved:
mptcp: syncookies: remember the request backup flag
Instead of using an uninitialised bit when copying the info in
subflow_ulp_clone().
To fix this, no need to extend the join_entry structure: backup is
coming from struct mptcp_subflow_request_sock, only one bit. Do the same
here by using one bit for both.
