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-misc.c

@@ -5,7 +5,7 @@
 #include "bus-error.h"
 #include "bus-locator.h"
 #include "fd-util.h"
-#include "format-util.h"
+#include "format-ifname.h"
 #include "netlink-util.h"
 #include "networkctl.h"
 #include "networkctl-misc.h"