Do not include if_var.h and in6_var.h into kern_jail.c. It is now possible

after r280444.

Sponsored by:	Nginx, Inc.

sys/kern/kern_jail.c

@@ -62,16 +62,12 @@ __FBSDID("$FreeBSD$");
 #include <sys/vnode.h>
 
 #include <net/if.h>
-#include <net/if_var.h>
 #include <net/vnet.h>
 
 #include <netinet/in.h>
 
 #ifdef DDB
 #include <ddb/ddb.h>
-#ifdef INET6
-#include <netinet6/in6_var.h>
-#endif /* INET6 */
 #endif /* DDB */
 
 #include <security/mac/mac_framework.h>