knfsd: change mailing list for nfsd in MAINTAINERS

nfs@lists.sourceforge.net is being decommissioned.

Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>