Increase the default socket buffer for NFS to deal with linux bugs and to

Increase the default socket buffer for NFS to deal with linux bugs and to
improve performance.   The default nfs socket buffer is now 65535 bytes,
settable with a sysctl (vfs.nfs.soreserve).

It is my belief that when large data block sizes (32K) are negotiated,
the larger socket buff should improve read-ahead performance and reduce
nfs socket buffer lock contention that occurs with multiple nfsd's.  I
was able to do some testing over GigE and it did seem to help, but problems
with one of the machines made the tests less then reliable.

Credits: Richard Sharpe originally encountered issues with linux NFS
clients that were traced to linux doing a bad job in its delayed-ack code.
David Rhodus created an initial patch which I used as a partial basis for
this commit (circa October 2003).