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/tests/channel/channel_test.c b/openbsc/tests/channel/channel_test.c
index 759001c..32c7168 100644
--- a/openbsc/tests/channel/channel_test.c
+++ b/openbsc/tests/channel/channel_test.c
@@ -76,6 +76,7 @@
 void nm_state_event() {}
 void input_event() {}
 void sms_alloc() {}
+void gsm_net_update_ctype(struct gsm_network *network) {}
 
 struct tlv_definition nm_att_tlvdef;