[IPV4]: Correct rp_filter help text.

As mentioned in http://bugzilla.kernel.org/show_bug.cgi?id=5015
The helptext implies that this is on by default.
This may be true on some distros (Fedora/RHEL have it enabled
in /etc/sysctl.conf), but the kernel defaults to it off.
Signed-off-by: NDave Jones <davej@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/Kconfig

@@ -43,11 +43,11 @@ config IP_ADVANCED_ROUTER
 	  asymmetric routing (packets from you to a host take a different path
 	  than packets from that host to you) or if you operate a non-routing
 	  host which has several IP addresses on different interfaces. To turn
-	  rp_filter off use:
+	  rp_filter on use:
 
-	  echo 0 > /proc/sys/net/ipv4/conf/<device>/rp_filter
+	  echo 1 > /proc/sys/net/ipv4/conf/<device>/rp_filter
 	  or
-	  echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter
+	  echo 1 > /proc/sys/net/ipv4/conf/all/rp_filter
 
 	  If unsure, say N here.