resolve: rename Link.name -> Link.ifname

This also changes the type from char[IF_NAMESIZE] to char*.
By changing the type, now resolved-link.h can drop the dependency to
the header net/if.h.

src/resolve/resolved-dns-server.c

@@ -836,7 +836,7 @@ void dns_server_dump(DnsServer *s, FILE *f) {
                 assert(s->link);
 
                 fputs(" interface=", f);
-                fputs(s->link->name, f);
+                fputs(s->link->ifname, f);
         }
 
         fputs("]\n", f);