[BUG] log: retrieve the target from the session, not the SI

Since we now have the copy of the target in the session, use it instead
of relying on the SI for it. The SI drops the target upon unregister()
so applets such as stats were logged as "NOSRV".
diff --git a/src/peers.c b/src/peers.c
index 739c09b..0274483 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -1078,6 +1078,7 @@
 {
 	 /* we have a dedicated I/O handler for the stats */
 	stream_int_register_handler(&s->si[1], &peer_applet);
+	copy_target(&s->target, &s->si[1].target); // for logging only
 	s->si[1].release = peer_session_release;
 	s->si[1].applet.private = s;
 	s->si[1].applet.st0 = PEER_SESSION_ACCEPT;