route(8): fix route not found exit code and warn with netlink

Fix route(8) incorrectly returning a zero exit code even when unable to
find the specified route with route -n get <route>.

PR:		274426
Reviewed by:	kp
Sponsored by:	Rubicon Communications, LLC ("Netgate")
Differential Revision:	https://reviews.freebsd.org/D41882

(cherry picked from commit 2a78083)

Author: rcmcdonald91

sbin/route/route_netlink.c

@@ -271,22 +271,27 @@ rtmsg_nl_int(struct nl_helper *h, int cmd, int rtm_flags, int fib, int rtm_addrs
 
 		hdr = snl_read_reply(ss, hdr->nlmsg_seq);
 		if (nl_type == NL_RTM_GETROUTE) {
-			if (hdr->nlmsg_type == NL_RTM_NEWROUTE)
+			if (hdr->nlmsg_type == NL_RTM_NEWROUTE) {
 				print_getmsg(h, hdr, dst);
-			else {
-				snl_parse_errmsg(ss, hdr, &e);
-				if (e.error == ESRCH)
-					warn("route has not been found");
-				else
-					warn("message indicates error %d", e.error);
+				return (0);
 			}
-
-			return (0);
 		}
 
-		if (snl_parse_errmsg(ss, hdr, &e))
+		if (snl_parse_errmsg(ss, hdr, &e)) {
+			switch (e.error) {
+			case (ESRCH):
+				warnx("route has not been found");
+				break;
+			default:
+				if (e.error == 0)
+					break;
+				warnc(e.error, "message indicates error");
+			}
+
 			return (e.error);
+		}
 	}
+
 	return (EINVAL);
 }