libnfs: Set as much stat information as possible

Set as much stat information as possible for stat, stat64, fstat and
readdir.

Fill in dev to the given fsid.
Fill in rdev to the given major and minor numbers.
Set the file type bits in the mode from the type returned by the server.
Set the number of blocks used based on the number of bytes used in
blocks of size 512 (which is what stat(2) uses), rounded up.
Fill in the nanosecond timestamps.

Signed-off-by: Ross Lagerwall <rosslagerwall@gmail.com>