[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 <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/netevent.h

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