nfsd: fix net-namespace logic in __nfsd_file_cache_purge

If the namespace doesn't match the one in "net", then we'll continue,
but that doesn't cause another rhashtable_walk_next call, so it will
loop infinitely.

Fixes: ce502f81 ("NFSD: Convert the filecache to use rhashtable")
Reported-by: Petr Vorel <pvorel@suse.cz>
Link: https://lore.kernel.org/ltp/Y1%2FP8gDAcWC%2F+VR3@pevik/Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/filecache.c

@@ -893,8 +893,7 @@ __nfsd_file_cache_purge(struct net *net)
 
 		nf = rhashtable_walk_next(&iter);
 		while (!IS_ERR_OR_NULL(nf)) {
-			if (net && nf->nf_net != net)
-				continue;
+			if (!net || nf->nf_net == net)
 				nfsd_file_unhash_and_dispose(nf, &dispose);
 			nf = rhashtable_walk_next(&iter);
 		}