BSC VTY: Allow encryption to be set to A5/3

We are currently not checking if the BTS actually suports that cipher,
and we particularly don't have any hack for ip.access which apparently
seems to re-use the RSL algorithm identifier for A5/2.
diff --git a/openbsc/src/libbsc/bsc_vty.c b/openbsc/src/libbsc/bsc_vty.c
index f306488..b38b08e 100644
--- a/openbsc/src/libbsc/bsc_vty.c
+++ b/openbsc/src/libbsc/bsc_vty.c
@@ -1174,10 +1174,11 @@
 
 DEFUN(cfg_net_encryption,
       cfg_net_encryption_cmd,
-      "encryption a5 (0|1|2)",
+      "encryption a5 (0|1|2|3)",
 	"Encryption options\n"
 	"A5 encryption\n" "A5/0: No encryption\n"
-	"A5/1: Encryption\n" "A5/2: Export-grade Encryption\n")
+	"A5/1: Encryption\n" "A5/2: Export-grade Encryption\n"
+	"A5/3: 'New' Secure Encryption\n")
 {
 	struct gsm_network *gsmnet = gsmnet_from_vty(vty);