gsm0808_utils: Add gsm0808_get_cipher_reject_cause() back with a deprecation notice.

In Change-Id Idf2b99e9ef014eba26e3d4f0f38c2714d3a0520a we accidentially removed this
symbol, let's re-introduce it.

Change-Id: I9fbcbcc6619ef0c63d3682fc86adc80045baab02
diff --git a/include/osmocom/gsm/gsm0808_utils.h b/include/osmocom/gsm/gsm0808_utils.h
index a8852e4..59db6ed 100644
--- a/include/osmocom/gsm/gsm0808_utils.h
+++ b/include/osmocom/gsm/gsm0808_utils.h
@@ -155,6 +155,9 @@
 	return (cause & 0x80) && !(cause & 0x0F);
 }
 
+int gsm0808_get_cipher_reject_cause(const struct tlv_parsed *tp)
+OSMO_DEPRECATED("Use gsm0808_get_cause() instead");
+
 /*! \returns 3GPP TS 48.008 3.2.2.49 Current Channel Type 1 from enum gsm_chan_t. */
 static inline uint8_t gsm0808_current_channel_type_1(enum gsm_chan_t type)
 {