nfsv3: simplify size3 object

Motivation:
size3 object is a wrap around uint64, which is by itself wrap around
long.

Modification:
simplify size3 by wrapping directly long

Result:
less load on GC.

Acked-by: Marina Sahakyan
Acked-by: Paul Millar
Target: master
1 job for master in 1 minute and 46 seconds (queued for 25 seconds)
Status Name Job ID Coverage
  Build
passed build #13566

00:01:46