Add an Android specific kernel_net_t implementation

This currently provides only no-ops and is just added because a
kernel-net implementation is required and kernel-netlink can't be used
at the moment.

src/frontends/android/jni/libandroidbridge/charonservice.h

@@ -18,6 +18,9 @@
 /**
  * @defgroup libandroidbridge libandroidbridge
  *
+ * @defgroup android_kernel kernel
+ * @ingroup libandroidbridge
+ *
  * @defgroup charonservice charonservice
  * @{ @ingroup libandroidbridge
  */