Rename OSMO_AUTH_ALG_XOR to OSMO_AUTH_ALG_XOR_3G

Let's disambiguate.  Our existing OSMO_AUTH_ALG_XOR was always only
the XOR-3G algorithm.  Now that we recently introduced XOR-2G,
let's rename (with backwards compatibility #define).

Change-Id: I446e54d0ddf4a18c46ee022b1249af73552e3ce1
diff --git a/include/osmocom/crypt/auth.h b/include/osmocom/crypt/auth.h
index 4af8ca8..d872f64 100644
--- a/include/osmocom/crypt/auth.h
+++ b/include/osmocom/crypt/auth.h
@@ -30,11 +30,14 @@
 	OSMO_AUTH_ALG_COMP128v1,
 	OSMO_AUTH_ALG_COMP128v2,
 	OSMO_AUTH_ALG_COMP128v3,
-	OSMO_AUTH_ALG_XOR,
+	OSMO_AUTH_ALG_XOR_3G,
 	OSMO_AUTH_ALG_MILENAGE,
 	OSMO_AUTH_ALG_XOR_2G,
 	_OSMO_AUTH_ALG_NUM,
 };
+/* Backwards-compatibility. We used to call XOR-3G just "XOR" which became ambiguous when
+ * we started to add XOR-2G support. */
+#define OSMO_AUTH_ALG_XOR OSMO_AUTH_ALG_XOR_3G
 
 /*! permanent (secret) subscriber auth data */
 struct osmo_sub_auth_data {