[TCP]: Fix TCP_OFF() bug check introduced by previous change.

The TCP_OFF assignment at the bottom of that if block can indeed set
TCP_OFF without setting TCP_PAGE.  Since there is not much to be
gained from avoiding this situation, we might as well just zap the
offset.  The following patch should fix it.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -769,10 +769,10 @@ int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 					if (off == PAGE_SIZE) {
 						put_page(page);
 						TCP_PAGE(sk) = page = NULL;
-						TCP_OFF(sk) = off = 0;
+						off = 0;
 					}
 				} else
-					BUG_ON(off);
+					off = 0;
 
 				if (copy > PAGE_SIZE - off)
 					copy = PAGE_SIZE - off;