ofproto: fix comment about ofproto-dpif

"dpif-netlink" is the dpif to communicate with kernel.
So replace "dpif-linux" with "dpif-netlink".

Signed-off-by: William Tu <u9012063@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

ofproto/ofproto-dpif.h

@@ -19,7 +19,7 @@
  *
  * 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.
  *