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/src/gsm/auth_xor.c b/src/gsm/auth_xor.c
index 4507542..81076bd 100644
--- a/src/gsm/auth_xor.c
+++ b/src/gsm/auth_xor.c
@@ -168,8 +168,8 @@
 }
 
 static struct osmo_auth_impl xor_alg = {
-	.algo = OSMO_AUTH_ALG_XOR,
-	.name = "XOR (libosmogsm built-in)",
+	.algo = OSMO_AUTH_ALG_XOR_3G,
+	.name = "XOR-3G (libosmogsm built-in)",
 	.priority = 1000,
 	.gen_vec = &xor_gen_vec,
 	.gen_vec_auts = &xor_gen_vec_auts,