Make apex availability to com.android.wifi explicit

The availability to wifi apex 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: I0aba19fb164690456d0bc36127e99b95a678775f
diff --git a/Android.bp b/Android.bp
index 1dd82b3..5e81599 100644
--- a/Android.bp
+++ b/Android.bp
@@ -206,6 +206,7 @@
     sdk_version: "core_current",
     min_sdk_version: "30",
     java_version: "1.7",
+    apex_available: ["com.android.wifi"],
 }
 
 // Bouncycastle PKIX classes in the original org.bouncycastle package for use