Use thunks for compat ioctls using struct ifgroupreq.

Reviewed by:	brooks, kib
Obtained from:	CheriBSD
Sponsored by:	DARPA
Differential Revision:	https://reviews.freebsd.org/D29893

newlib/libc/sys/rtems/include/net/if.h

@@ -530,10 +530,8 @@ struct ifgroupreq {
 		char	ifgru_group[IFNAMSIZ];
 		struct	ifg_req *ifgru_groups;
 	} ifgr_ifgru;
-#ifndef _KERNEL
 #define ifgr_group	ifgr_ifgru.ifgru_group
 #define ifgr_groups	ifgr_ifgru.ifgru_groups
-#endif
 };
 
 /*