SUNRPC: remove machine_cred field from struct auth_cred

The cred is a machine_cred iff ->principal is set, so there is no
need for the extra flag.

There is one case which deserves some
explanation. nfs4_root_machine_cred() calls rpc_lookup_machine_cred()
with a NULL principal name which results in not getting a machine
credential, but getting a root credential instead.
This appears to be what is expected of the caller, and is
clearly the result provided by both auth_unix and auth_gss
which already ignore the flag.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
diff --git a/include/linux/sunrpc/auth.h b/include/linux/sunrpc/auth.h
index 831ea65..1c0468f 100644
--- a/include/linux/sunrpc/auth.h
+++ b/include/linux/sunrpc/auth.h
@@ -46,9 +46,8 @@ enum {
 
 struct auth_cred {
 	const struct cred *cred;
-	const char *principal;
+	const char *principal;	/* If present, this is a machine credential */
 	unsigned long ac_flags;
-	unsigned char machine_cred : 1;
 };
 
 /*