Use own format to specify encryption algorithm

... instead of using the one from from osmo vty directly.

This way we avoid having multiple word attribute value and we can skip
using quotes in the conf files.

Change-Id: I5265cc9990dd5e99dba1f6262b3a8c597a3e958d
diff --git a/example/defaults.conf b/example/defaults.conf
index f6ecedd..e2921a4 100644
--- a/example/defaults.conf
+++ b/example/defaults.conf
@@ -5,7 +5,7 @@
     short_name: osmo-gsm-tester-nitb
     long_name: osmo-gsm-tester-nitb
     auth_policy: closed
-    encryption: a5 0
+    encryption: a5_0
 
 bsc:
   net:
@@ -14,7 +14,7 @@
     short_name: osmo-gsm-tester-msc
     long_name: osmo-gsm-tester-msc
     auth_policy: closed
-    encryption: a5 0
+    encryption: a5_0
     authentication: optional
 
 msc:
@@ -24,7 +24,7 @@
     short_name: osmo-gsm-tester-msc
     long_name: osmo-gsm-tester-msc
     auth_policy: closed
-    encryption: a5 0
+    encryption: a5_0
     authentication: optional
 
 bsc_bts: