Introduce support for XOR-2G algorithm

So far we supported a "xor" algorithm in osmo-hlr, without specifying
whether it's the XOR-3G or the (different) XOR-2G algorithm.

Furthermore, it was buggy in the sense that it permitted the XOR[-3G]
for 2G authentication data in the database.

This patch
* renames existing "xor" to "xor-3g"
* disallows "xor-3g" usage with 2G authentication data
* introduces support for XOR-2G as "xor-2g" in the VTY

Change-Id: I039a1f84fda54a908a82fe621e7fd078cb85e4c6
Depends: libosmocore.git I0ee0565382c1e4515d44ff9b1752685c0a66ae39
diff --git a/tests/test_subscriber_errors.ctrl b/tests/test_subscriber_errors.ctrl
index 6b1ade6..4603a77 100644
--- a/tests/test_subscriber_errors.ctrl
+++ b/tests/test_subscriber_errors.ctrl
@@ -130,7 +130,7 @@
 SET 55 subscriber.by-imsi-901990000000003.aud2g foobar,2134
 ERROR 55 Unknown auth algorithm.
 
-SET 56 subscriber.by-imsi-901990000000003.aud2g xor,2134
+SET 56 subscriber.by-imsi-901990000000003.aud2g xor-2g,2134
 ERROR 56 Invalid KI.
 
 SET 57 subscriber.by-imsi-901990000000003.aud3g foobar