mscsplit: directly access gsm_network backpointer from gsm_subscriber_connection

The previous commit added a network backpointer to gsm_subscriber_connection.
Use it wherever it makes sense, to skip the step through the bts structure.

In some places, remove local variables that become unused.

Change-Id: I34537025986713291e14c8212a81539b497befd4
diff --git a/openbsc/src/libbsc/bsc_api.c b/openbsc/src/libbsc/bsc_api.c
index 02751f4..cc12e9f 100644
--- a/openbsc/src/libbsc/bsc_api.c
+++ b/openbsc/src/libbsc/bsc_api.c
@@ -146,7 +146,7 @@
 	conn->secondary_lchan = NULL;
 
 	/* inform them about the failure */
-	api = conn->bts->network->bsc_api;
+	api = conn->network->bsc_api;
 	api->assign_fail(conn, GSM0808_CAUSE_NO_RADIO_RESOURCE_AVAILABLE, NULL);
 }
 
@@ -157,7 +157,7 @@
 			     struct gsm_lchan *lchan, int full_rate)
 {
 	struct bsc_api *api;
-	api = conn->bts->network->bsc_api;
+	api = conn->network->bsc_api;
 	struct amr_multirate_conf *mr;
 	struct gsm48_multi_rate_conf *mr_conf;
 
@@ -387,7 +387,7 @@
 int gsm0808_assign_req(struct gsm_subscriber_connection *conn, int chan_mode, int full_rate)
 {
 	struct bsc_api *api;
-	api = conn->bts->network->bsc_api;
+	api = conn->network->bsc_api;
 
 	if (!chan_compat_with_mode(conn->lchan, chan_mode, full_rate)) {
 		if (handle_new_assignment(conn, chan_mode, full_rate) != 0)
@@ -424,7 +424,7 @@
 			     struct msgb *msg)
 {
 	struct gsm48_hdr *gh;
-	struct bsc_api *api = conn->bts->network->bsc_api;
+	struct bsc_api *api = conn->network->bsc_api;
 
 	if (conn->secondary_lchan != msg->lchan) {
 		LOGP(DMSC, LOGL_ERROR, "Assignment Compl should occur on second lchan.\n");
@@ -461,7 +461,7 @@
 static void handle_ass_fail(struct gsm_subscriber_connection *conn,
 			    struct msgb *msg)
 {
-	struct bsc_api *api = conn->bts->network->bsc_api;
+	struct bsc_api *api = conn->network->bsc_api;
 	uint8_t *rr_failure;
 	struct gsm48_hdr *gh;
 
@@ -751,7 +751,7 @@
 	if (!conn)
 		return;
 
-	api = conn->bts->network->bsc_api;
+	api = conn->network->bsc_api;
 	if (!api || !api->sapi_n_reject)
 		return;