Propagate SYN handling error
Propagate SYN handling error

Both callers of this function still drop this error on the floor, but
progress is progress.

Updates #4690.

PiperOrigin-RevId: 367604788

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor