CVE-2025-71088 mptcp: fallback earlier on simult connection

In the Linux kernel, the following vulnerability has been resolved: mptcp: fallback earlier on simult connection Syzkaller reports a simult-connect race leading to inconsistent fallback status: WARNING: CPU: 3 PID: 33 at net/mptcp/subflow.c:1515 subflowdataready+0x40b/0x7c0 net/mptcp/subflow.c:15...