smb: client: improve DFS mount check

Some servers may return error codes from REQ_GET_DFS_REFERRAL requests
that are unexpected by the client, so to make it easier, assume
non-DFS mounts when the client can't get the initial DFS referral of
@ctx->UNC in dfs_mount_share().

Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/dfs.c

@@ -264,8 +264,9 @@ int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs)
 	if (!nodfs) {
 		rc = dfs_get_referral(mnt_ctx, ctx->UNC + 1, NULL, NULL);
 		if (rc) {
-			if (rc != -ENOENT && rc != -EOPNOTSUPP && rc != -EIO)
-				return rc;
+			cifs_dbg(FYI, "%s: no dfs referral for %s: %d\n",
+				 __func__, ctx->UNC + 1, rc);
+			cifs_dbg(FYI, "%s: assuming non-dfs mount...\n", __func__);
 			nodfs = true;
 		}
 	}