gsm0808: Move the clear request from bsc_msc_ip to here

This method should use the msgb_tlv_put routines instead
of the stuff it is doing. This will be cleaned up.
diff --git a/include/osmocore/gsm0808.h b/include/osmocore/gsm0808.h
index c6d11e1..1d85377 100644
--- a/include/osmocore/gsm0808.h
+++ b/include/osmocore/gsm0808.h
@@ -36,6 +36,7 @@
 						 uint8_t chosen_channel, uint8_t encr_alg_id,
 						 uint8_t speech_mode);
 struct msgb *gsm0808_create_assignment_failure(uint8_t cause, uint8_t *rr_cause);
+struct msgb *gsm0808_create_clear_rqst(uint8_t cause);
 
 struct msgb *gsm0808_create_dtap(struct msgb *msg, uint8_t link_id);
 void gsm0808_prepend_dtap_header(struct msgb *msg, uint8_t link_id);