SUNRPC: Add a generic RPC credential

Add an rpc credential that is not tied to any particular auth mechanism,
but that can be cached by NFS, and later used to look up a cred for
whichever auth mechanism that turns out to be valid when the RPC call is
being made.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/auth.c

@@ -566,6 +566,7 @@ static struct shrinker rpc_cred_shrinker = {
 void __init rpcauth_init_module(void)
 {
 	rpc_init_authunix();
+	rpc_init_generic_auth();
 	register_shrinker(&rpc_cred_shrinker);
 }