ofproto: fix comment about ofproto-dpif
"dpif-netlink" is the dpif to communicate with kernel.
So replace "dpif-linux" with "dpif-netlink".
*
* ofproto-dpif provides an ofproto implementation for those platforms which
* implement the netdev and dpif interface defined in netdev.h and dpif.h. The
- * most important of which is the Linux Kernel Module (dpif-linux), but
+ * most important of which is the Linux Kernel Module (dpif-netlink), but
* alternatives are supported such as a userspace only implementation
* (dpif-netdev), and a dummy implementation used for unit testing.
*
