crypto: increase default pbkdf2 time for luks to 2 seconds

cryptsetup recently increased the default pbkdf2 time to 2 seconds
to partially mitigate improvements in hardware performance wrt
brute-forcing the pbkdf algorithm. This updates QEMU defaults to
match.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
diff --git a/qapi/crypto.json b/qapi/crypto.json
index 2b6118f..6933b13 100644
--- a/qapi/crypto.json
+++ b/qapi/crypto.json
@@ -187,7 +187,7 @@
 #            Currently defaults to 'sha256'
 # @iter-time: #optional number of milliseconds to spend in
 #             PBKDF passphrase processing. Currently defaults
-#             to 1000. (since 2.8)
+#             to 2000. (since 2.8)
 # Since: 2.6
 ##
 { 'struct': 'QCryptoBlockCreateOptionsLUKS',