bsc_api: Do not free the subscriber conn on clear and clear request

Do not free the GSM Subscriber Connection when a channel is failing
or if a clear is requested, instead just give up _all_ the channels,
reset them to NULL and free the remaining channels.
diff --git a/openbsc/src/osmo_msc.c b/openbsc/src/osmo_msc.c
index 6543a61..97f36f5 100644
--- a/openbsc/src/osmo_msc.c
+++ b/openbsc/src/osmo_msc.c
@@ -92,4 +92,5 @@
 	/* no more connections, asking to release the channel */
 	conn->in_release = 1;
 	gsm0808_clear(conn);
+	subscr_con_free(conn);
 }