route: Fix flush w/o specified address family

PR:		291867
Reported by:	gavin
Reviewed by:	pouria, melifaro
Sponsored by:	The FreeBSD Foundation
Fixes: c597432e22 ("route(8): convert to netlink")
Differential Revision: https://reviews.freebsd.org/D57336

sbin/route/route_netlink.c

@@ -950,7 +950,8 @@ flushroutes_fib_nl(int fib, int af)
 			struct snl_msg_info attrs = {};
 			print_nlmsg(&h, hdr, &attrs);
 		}
-		if (r.rta_table != (uint32_t)fib || r.rtm_family != af)
+		if (r.rta_table != (uint32_t)fib ||
+		    (af != AF_UNSPEC && r.rtm_family != af))
 			continue;
 		if ((r.rta_rtflags & RTF_GATEWAY) == 0)
 			continue;