nfsd: Fix NFSv3 Readdir/ReaddirPlus reply for large i-node numbers

If the i-node number (d_fileno) for a file on the server did
not fit in 32bits, it would be truncated to the low order 32bits
for the NFSv3 Readdir and ReaddirPlus RPC replies.
This is no longer correct, given that ino_t is now 64bits.

This patch fixes this by sending the full 64bits of d_fileno
on the wire in the NFSv3 Readdir/ReaddirPlus RPC reply.

PR: 271174
Reported by: bmueller@panasas.com
Tested by: bmueller@panasas.com
MFC after: 2 weeks