Fix: install flattened apex on system_ext

This build rule is specific to platform APEXes.
For non-platform APEXes, MakeAsSystemExt() is not applied.

This fixes the cases of "soc_specific: true" apexes which fails to
build.

Bug: 139053989
Test: m nothing (soong tests)
Change-Id: I98d0257499647ab41cdaa62a3671d89addbdf833
Exempt-From-Owner-Approval: got +1 before rebasing
diff --git a/android/module.go b/android/module.go
index 891babc..d5c8b98 100644
--- a/android/module.go
+++ b/android/module.go
@@ -1515,9 +1515,11 @@
 }
 
 func (m *ModuleBase) MakeAsSystemExt() {
-	if !Bool(m.commonProperties.Vendor) && !Bool(m.commonProperties.Product_specific) {
-		m.commonProperties.System_ext_specific = boolPtr(true)
-	}
+	m.commonProperties.Vendor = boolPtr(false)
+	m.commonProperties.Proprietary = boolPtr(false)
+	m.commonProperties.Soc_specific = boolPtr(false)
+	m.commonProperties.Product_specific = boolPtr(false)
+	m.commonProperties.System_ext_specific = boolPtr(true)
 }
 
 // IsNativeBridgeSupported returns true if "native_bridge_supported" is explicitly set as "true"