iodined service: wantedBy ip-up.target

When iodined tries to start before any interface other than loopback has an ip, iodined fails.
Wait for ip-up.target

The above is because of the following:
in iodined's code: src/common.c line 157
	the flag AI_ADDRCONFIG is passed as a flag to getaddrinfo.
	Iodine uses the function

		get_addr(char *host,
			int port,
			int addr_family,
			int flags,
			struct sockaddr_storage *out);

	to get address information via getaddrinfo().

	Within get_addr, the flag AI_ADDRCONFIG is forced.

	What this flag does, is cause getaddrinfo to return
	"Name or service not known" as an error explicitly if no ip
	has been assigned to the computer.
	see getaddrinfo(3)

Wait for an ip before starting iodined.

nixos/modules/services/networking/iodined.nix

@@ -64,8 +64,7 @@ in
 
     systemd.services.iodined = {
       description = "iodine, ip over dns daemon";
-      after = [ "network.target" ];
-      wantedBy = [ "multi-user.target" ];
+      wantedBy = [ "ip-up.target" ];
       serviceConfig.ExecStart = "${pkgs.iodine}/sbin/iodined -f -u ${iodinedUser} ${cfg.extraConfig} ${cfg.ip} ${cfg.domain}";
     };