nfsd: pass proper net to nfsd_destroy() from NFSd kthreads

nfsd: pass proper net to nfsd_destroy() from NFSd kthreads

commit 88c47666171989ed4c5b1a5687df09511e8c5e35 upstream.

Since NFSd service is per-net now, we have to pass proper network
context in nfsd_shutdown() from NFSd kthreads.

The simplest way I found is to get proper net from one of transports
with permanent sockets.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
[wengmeiling: backport to 3.4: adjust context]
Signed-off-by: Weng Meiling <wengmeiling.weng@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>