basic: split ifname related calls from format-util.h into format-ifname.h

This way we don't have to pull in net/if.h into format-util.h.

This is supposed to address https://github.com/systemd/systemd/pull/32212#discussion_r1755639881

No actual code changes, just a .c/.h file split-up.

src/network/networkctl-dump-util.c

@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
-#include "format-util.h"
+#include "format-ifname.h"
 #include "in-addr-util.h"
 #include "local-addresses.h"
 #include "networkctl-dump-util.h"