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/machine/machinectl.c

@@ -32,6 +32,7 @@
 #include "edit-util.h"
 #include "env-util.h"
 #include "fd-util.h"
+#include "format-ifname.h"
 #include "format-table.h"
 #include "hostname-util.h"
 #include "import-util.h"