ipv4: minor fix about RPF in help of Kconfig

Signed-off-by: NNicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/Kconfig

@@ -46,7 +46,7 @@ config IP_ADVANCED_ROUTER
 	  rp_filter on use:
 
 	  echo 1 > /proc/sys/net/ipv4/conf/<device>/rp_filter
-	   and
+	   or
 	  echo 1 > /proc/sys/net/ipv4/conf/all/rp_filter
 
 	  Note that some distributions enable it in startup scripts.