Use Shell.Interactive interactively and removes iptables submodule

The following action will take only one SU request with this commit:

* Start service in NAT mode;
* Reset in NAT mode;
* Flush DNS.

And stopping service in NAT mode doesn't need SU request any more.

.gitmodules

@@ -5,10 +5,6 @@
 	path = src/main/jni/badvpn
 	url = https://github.com/shadowsocks/badvpn.git
 	branch = shadowsocks-android
-[submodule "src/main/jni/iptables"]
-	path = src/main/jni/iptables
-	url = https://github.com/shadowsocks/iptables.git
-	branch = shadowsocks-android
 [submodule "src/main/jni/libancillary"]
 	path = src/main/jni/libancillary
 	url = https://github.com/shadowsocks/libancillary.git