Don't hold MM.activeMu when calling MM.vmaMapsEntryLocked().
Don't hold MM.activeMu when calling MM.vmaMapsEntryLocked().

Cloned from CL 446797388 by 'hg patch'.

PiperOrigin-RevId: 454742145

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