Make apex availability of ksoap2 explicit

The availability to com.android.wifi was done implicitly using a baseline map in
build/soong/apex/apex.go. Make this explicit in Android.bp

Bug: 281077552
Test: m nothing
Change-Id: I25755e78d72361f02cd3ef3121896b4e81dbd975
diff --git a/Android.bp b/Android.bp
index c3f6393..7a91b65 100644
--- a/Android.bp
+++ b/Android.bp
@@ -33,4 +33,5 @@
     sdk_version: "system_current",
     min_sdk_version: "30",
     srcs: ["**/*.java"],
+    apex_available: ["com.android.wifi"],
 }