SUNRPC: Don't return EPROTONOSUPPORT in svc_register()'s helpers

The RPC client returns -EPROTONOSUPPORT if there is a protocol version
mismatch (ie the remote RPC server doesn't support the RPC protocol
version sent by the client).

Helpers for the svc_register() function return -EPROTONOSUPPORT if they
don't recognize the passed-in IPPROTO_ value.

These are two entirely different failure modes.

Have the helpers return -ENOPROTOOPT instead of -EPROTONOSUPPORT.  This
will allow callers to determine more precisely what the underlying
problem is, and decide to report or recover appropriately.

This patch is part of a series that addresses
   http://bugzilla.kernel.org/show_bug.cgi?id=12256

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/svc.c

@@ -749,7 +749,7 @@ static int __svc_rpcb_register4(const u32 program, const u32 version,
 		netid = RPCBIND_NETID_TCP;
 		break;
 	default:
-		return -EPROTONOSUPPORT;
+		return -ENOPROTOOPT;
 	}
 
 	return rpcb_v4_register(program, version,
@@ -785,7 +785,7 @@ static int __svc_rpcb_register6(const u32 program, const u32 version,
 		netid = RPCBIND_NETID_TCP6;
 		break;
 	default:
-		return -EPROTONOSUPPORT;
+		return -ENOPROTOOPT;
 	}
 
 	return rpcb_v4_register(program, version,