NFS: Use proper naming conventions for nfs_client.impl_id field

Clean up:  When naming fields and data types, follow established
conventions to facilitate accurate grep/cscope searches.

Additionally, for consistency, move the impl_id field into the NFSv4-
specific part of the nfs_client, and free that memory in the logic
that shuts down NFSv4 nfs_clients.

Introduced by commit 7d2ed9ac "NFSv4: parse and display server
implementation ids," Fri Feb 17, 2012.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index a973eb1..ff656c0 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -796,8 +796,8 @@
 
 static void show_implementation_id(struct seq_file *m, struct nfs_server *nfss)
 {
-	if (nfss->nfs_client && nfss->nfs_client->impl_id) {
-		struct nfs41_impl_id *impl_id = nfss->nfs_client->impl_id;
+	if (nfss->nfs_client && nfss->nfs_client->cl_implid) {
+		struct nfs41_impl_id *impl_id = nfss->nfs_client->cl_implid;
 		seq_printf(m, "\n\timpl_id:\tname='%s',domain='%s',"
 			   "date='%llu,%u'",
 			   impl_id->name, impl_id->domain,