chan: Store the to be assigned channel type in the GSM Network.

Store the mapping from request to channel type in the GSM Network
struct as there is some policy involved with handling the request.

E.g. in a half rate network we don't want emergy calls to be getting
a TCH/F, or we want to have a different policy for early/late assignment
of phone calls. Update the table when creating the network and when
the neci is changed.
diff --git a/openbsc/src/bs11_config.c b/openbsc/src/bs11_config.c
index 44cef0a..71e4aed 100644
--- a/openbsc/src/bs11_config.c
+++ b/openbsc/src/bs11_config.c
@@ -872,3 +872,8 @@
 
 	exit(0);
 }
+
+/* dummy to be able to compile */
+void gsm_net_update_ctype(struct gsm_network *net)
+{
+}