tree-wide: Various forward header cleanups

- Make sure forward headers have the iwyu pragma to always keep them
- Make sure we always include the daemon specific forward header
  instead of shared-forward.h
- Remove shared-forward.h include where the daemon specific forward
  header is already included

src/network/networkd-address.h

@@ -2,7 +2,6 @@
 #pragma once
 
 #include "firewall-util.h"
-#include "shared-forward.h"
 #include "in-addr-util.h"
 #include "networkd-forward.h"
 #include "networkd-util.h"

src/network/networkd-bridge-fdb.h

@@ -8,7 +8,6 @@
 #include <linux/neighbour.h>
 #include <net/ethernet.h>
 
-#include "shared-forward.h"
 #include "in-addr-util.h"
 #include "networkd-forward.h"
 

src/network/networkd-forward.h

@@ -1,6 +1,8 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+/* IWYU pragma: always_keep */
+
 #include "conf-parser-forward.h"    /* IWYU pragma: export */
 #include "shared-forward.h"         /* IWYU pragma: export */
 

src/network/networkd-link.h

@@ -4,7 +4,6 @@
 #include <linux/nl80211.h>
 
 #include "ether-addr-util.h"
-#include "shared-forward.h"
 #include "network-util.h"
 #include "networkd-bridge-vlan.h"
 #include "networkd-forward.h"