fscrypt: make test_dummy_encryption use v2 by default

Since v1 encryption policies are deprecated, make test_dummy_encryption
test v2 policies by default.

Note that this causes ext4/023 and ext4/028 to start failing due to
known bugs in those tests (see previous commit).

Link: https://lore.kernel.org/r/20200512233251.118314-5-ebiggers@kernel.org
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>

fs/crypto/policy.c

@@ -643,7 +643,7 @@ int fscrypt_set_test_dummy_encryption(struct super_block *sb,
 				      const substring_t *arg,
 				      struct fscrypt_dummy_context *dummy_ctx)
 {
-	const char *argstr = "v1";
+	const char *argstr = "v2";
 	const char *argstr_to_free = NULL;
 	struct fscrypt_key_specifier key_spec = { 0 };
 	int version;