rust/crypto: Add key_type method to SymKey impl

This function is easier to be used than a match! statement.
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>

rust/pv/src/crypto.rs

@@ -82,6 +82,14 @@ impl SymKey {
             Self::Aes256Xts(key) => key.value(),
         }
     }
+
+    /// Return the key type of this [`SymKey`].
+    pub fn key_type(&self) -> SymKeyType {
+        match self {
+            Self::Aes256(_) => SymKeyType::Aes256,
+            Self::Aes256Xts(_) => SymKeyType::Aes256Xts,
+        }
+    }
 }
 
 impl From<Aes256Key> for SymKey {
@@ -512,4 +520,16 @@ mod tests {
             Nid::AES_256_XTS
         );
     }
+
+    #[test]
+    fn key_type() {
+        assert_eq!(
+            SymKey::random(SymKeyType::Aes256).unwrap().key_type(),
+            SymKeyType::Aes256
+        );
+        assert_eq!(
+            SymKey::random(SymKeyType::Aes256Xts).unwrap().key_type(),
+            SymKeyType::Aes256Xts
+        );
+    }
 }