NFS - Properly handle NFSv3 EOF short-reads
* Short reads were not causing the remainder of the buffer to be
zero'd out in all cases, causing the fsx filesystem test to fail.
* An EOF condition was sometimes improperly reporting a non-zero
bp->b_resid. Race against the server where the client's idea of
the file size differs from the server could result in a non-zero
bp->b_resid after a BIO.
Zero out the remaining space and and set bp->b_resid to 0. The
NFS client code always specifies buffers within the bounds of
the file.
Reported-by: Antonio Huete Jimenez <tuxillo@quantumachine.net>