KeyMint VTS: test default MGF_DIGEST behaviour

KeyMint supports the specification of a separate MGF digest when
performing RSA-OAEP decryption, with a default value of SHA-1.

Test the expected behaviour here:
 - SHA-1 is used if nothing specified in key characteristics.
 - If something is specified in key characteristics, the operation
   parameter value has to be one of those values.

Bug: 203688354
Test: VtsAidlKeyMintTargetTest
Change-Id: Ic2dd3641be732a273724faa20cf4edf8a1752506
diff --git a/security/keymint/aidl/vts/functional/KeyMintAidlTestBase.cpp b/security/keymint/aidl/vts/functional/KeyMintAidlTestBase.cpp
index 46db4f0..37371c0 100644
--- a/security/keymint/aidl/vts/functional/KeyMintAidlTestBase.cpp
+++ b/security/keymint/aidl/vts/functional/KeyMintAidlTestBase.cpp
@@ -981,7 +981,7 @@
 
     // Retrieve relevant tags.
     Digest digest = Digest::NONE;
-    Digest mgf_digest = Digest::NONE;
+    Digest mgf_digest = Digest::SHA1;
     PaddingMode padding = PaddingMode::NONE;
 
     auto digest_tag = params.GetTagValue(TAG_DIGEST);