m_sethost.c
change requirement that remote sethost comes from U:lined server
to require that it comes from a service server (+s flag)

m_mode.c
change that mode changes by service server (+s flag) goes to HACK4
other server mode changes to HACK3
(was U:lined server to HACK4, else HACK3)

U:lined - we need learn what this does nowadays.

Other than the HACK4 or HACK3 choice, there seems to be something with
server introduction (a U:lined server is not allowed to introduce a new server
when that leads to a loop?) and also, any downlinks a U:lined server has
are also marked as U:lined.

No other differences found for U:lined vs. non-U:lined servers.

diff -r 7550bca292f5 ircd/m_mode.c
--- a/ircd/m_mode.c
+++ b/ircd/m_mode.c
@@ -212,7 +212,7 @@
   ClrFlag(sptr, FLAG_TS8);
 
   if (IsServer(sptr)) {
-    if (find_conf_byhost(cli_confs(cptr), cli_name(sptr), CONF_UWORLD))
+    if (IsService(sptr)) /* server is a service so HACK4 */
       modebuf_init(&mbuf, sptr, cptr, chptr,
 		   (MODEBUF_DEST_CHANNEL | /* Send mode to clients */
 		    MODEBUF_DEST_SERVER  | /* Send mode to servers */