Writing the notification must be synchronized with closing the FUSE
connection.

6g has changed its baseaddress. Users that require small inode numbers
should just use portableHandleMap.

look like a race condition.

It had a race condition. Removing it frees us from having go-routines
hanging around after the FS is unmounted.

in the mount.

On T60, for each file we have
- Client side latency is 360us
- 106us of this is server side latency (4.5x lookup 23us, 1x getattr 4us) 
- 16.5us is due to latency measurement (time.Now() calls)
- 3us is due to garbage collection.