ksoap2: Compile against system_current

Required since wifi is linking against this library.

Bug: 145935469
Test: Compiles
Change-Id: Iafdec0e2c3e17c7e9d1384fac072cdc9ae2ff4a7
diff --git a/Android.bp b/Android.bp
index 2ac1227..2075b81 100644
--- a/Android.bp
+++ b/Android.bp
@@ -1,4 +1,5 @@
 java_library {
     name: "ksoap2",
+    sdk_version: "system_current",
     srcs: ["**/*.java"],
 }