gsm0808: add gsm0808_create_sapi_reject_cause()

This is basically a successor of gsm0808_create_sapi_reject(), but
instead of hard-coding GSM0808_CAUSE_BSS_NOT_EQUIPPED, it allows
the caller to specify a cause value to be used.  The old function
is now deprecated and should not be used.

Change-Id: Iefe5484d0fa02d5722b628b1dc237d51d3fb1a9b
Related: OS#4728
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 713ffe3..4ece107 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -190,6 +190,7 @@
 gsm0808_create_lcls_notification;
 gsm0808_create_reset;
 gsm0808_create_reset_ack;
+gsm0808_create_sapi_reject_cause;
 gsm0808_create_sapi_reject;
 gsm0808_create_handover_required;
 gsm0808_create_handover_required_reject;