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/resolve/resolvectl.c

@@ -20,8 +20,8 @@
 #include "dns-domain.h"
 #include "errno-list.h"
 #include "escape.h"
+#include "format-ifname.h"
 #include "format-table.h"
-#include "format-util.h"
 #include "gcrypt-util.h"
 #include "hostname-util.h"
 #include "json-util.h"

src/resolve/resolved-dns-cache.c

@@ -5,7 +5,7 @@
 #include "af-list.h"
 #include "alloc-util.h"
 #include "dns-domain.h"
-#include "format-util.h"
+#include "format-ifname.h"
 #include "resolved-dns-answer.h"
 #include "resolved-dns-cache.h"
 #include "resolved-dns-packet.h"