Revert "rose: zero length frame filtering in af_rose.c"

This reverts commit 244f46ae6e9e18f6fc0be7d1f49febde4762c34b.

Alan Cox did the research, and just like the other radio protocols
zero-length frames have meaning because at the top level ROSE is
X.25 PLP.

So this zero-length filtering is invalid.

Signed-off-by: David S. Miller <davem@davemloft.net>

net/rose/af_rose.c

@@ -1072,10 +1072,6 @@ static int rose_sendmsg(struct kiocb *iocb, struct socket *sock,
 	unsigned char *asmptr;
 	int n, size, qbit = 0;
 
-	/* ROSE empty frame has no meaning : don't send */
-	if (len == 0)
-		return 0;
-
 	if (msg->msg_flags & ~(MSG_DONTWAIT|MSG_EOR|MSG_CMSG_COMPAT))
 		return -EINVAL;
 
@@ -1273,12 +1269,6 @@ static int rose_recvmsg(struct kiocb *iocb, struct socket *sock,
 	skb_reset_transport_header(skb);
 	copied     = skb->len;
 
-	/* ROSE empty frame has no meaning : ignore it */
-	if (copied == 0) {
-		skb_free_datagram(sk, skb);
-		return copied;
-	}
-
 	if (copied > size) {
 		copied = size;
 		msg->msg_flags |= MSG_TRUNC;