Unlock tcp endpoint mutex before blocking forever.
Unlock tcp endpoint mutex before blocking forever.

This was occasionally causing tests to get stuck due to races with the save
process, during which the same mutex is acquired.

PiperOrigin-RevId: 340789616

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