Revert: lockd: use rpc client's cl_nodename for id encoding

This reverts 12d63702c53bc2230dfc997e91ca891f39cb6446 which was commit
303a7ce92064c285a04c870f2dc0192fdb2968cb upstream.

Taking hostname from uts namespace if not safe, because this cuold be
performind during umount operation on child reaper death. And in this case
current->nsproxy is NULL already.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Stanislav Kinsbursky <skinsbursky@parallels.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>