SUNRPC: Use MSG_SENDPAGE_NOTLAST in xs_send_pagedata()

If we're sending more than one page via kernel_sendpage(), then set
MSG_SENDPAGE_NOTLAST between the pages so that we don't send suboptimal
frames (see commit 2f5338442425 and commit 35f9c09fe9c7).

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

net/sunrpc/xprtsock.c

@@ -360,8 +360,10 @@ static int xs_send_pagedata(struct socket *sock, struct xdr_buf *xdr, unsigned i
 		int flags = XS_SENDMSG_FLAGS;
 
 		remainder -= len;
-		if (remainder != 0 || more)
+		if (more)
 			flags |= MSG_MORE;
+		if (remainder != 0)
+			flags |= MSG_SENDPAGE_NOTLAST | MSG_MORE;
 		err = do_sendpage(sock, *ppage, base, len, flags);
 		if (remainder == 0 || err != len)
 			break;