[NET]: Remove unnecessary inclusion of dst.h

The file net/netevent.h only refers to struct dst_entry * so it
doesn't need to include dst.h.  I've replaced it with a forward
declaration.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netevent.h

@@ -12,7 +12,7 @@
  */
 #ifdef __KERNEL__
 
-#include <net/dst.h>
+struct dst_entry;
 
 struct netevent_redirect {
 	struct dst_entry *old;