gsm0808: Make a function to extract Cause IE publicly available.

Function gsm0808_get_cipher_reject_cause() was previously available
in private gsm0808_utils.h. In practice, the exact same code is useful
to extract Cause IE value from any of the many other BSSMAP messages
which use it.

So let's rename it to gsm0808_get_cause() and make it avilable
to everyone to use.

Change-Id: Idf2b99e9ef014eba26e3d4f0f38c2714d3a0520a
diff --git a/src/gsm/gsm0808.c b/src/gsm/gsm0808.c
index 02288e6..788f6c3 100644
--- a/src/gsm/gsm0808.c
+++ b/src/gsm/gsm0808.c
@@ -1654,6 +1654,22 @@
 	return get_value_string(gsm0808_cause_names, cause);
 }
 
+enum gsm0808_cause gsm0808_get_cause(const struct tlv_parsed *tp)
+{
+	const uint8_t *buf = TLVP_VAL_MINLEN(tp, GSM0808_IE_CAUSE, 1);
+
+	if (!buf)
+		return -EBADMSG;
+
+	if (TLVP_LEN(tp, GSM0808_IE_CAUSE) > 1) {
+		if (!gsm0808_cause_ext(buf[0]))
+			return -EINVAL;
+		return buf[1];
+	}
+
+	return buf[0];
+}
+
 const struct value_string gsm0808_lcls_config_names[] = {
 	{ GSM0808_LCLS_CFG_BOTH_WAY, "Connect both-way" },
 	{ GSM0808_LCLS_CFG_BOTH_WAY_AND_BICAST_UL,
diff --git a/src/gsm/gsm0808_utils.c b/src/gsm/gsm0808_utils.c
index 7416d8f..6f3c07a 100644
--- a/src/gsm/gsm0808_utils.c
+++ b/src/gsm/gsm0808_utils.c
@@ -1563,22 +1563,6 @@
 	return 0;
 }
 
-int gsm0808_get_cipher_reject_cause(const struct tlv_parsed *tp)
-{
-	const uint8_t *buf = TLVP_VAL_MINLEN(tp, GSM0808_IE_CAUSE, 1);
-
-	if (!buf)
-		return -EBADMSG;
-
-	if (TLVP_LEN(tp, GSM0808_IE_CAUSE) > 1) {
-		if (!gsm0808_cause_ext(buf[0]))
-			return -EINVAL;
-		return buf[1];
-	}
-
-	return buf[0];
-}
-
 /*! Print a human readable name of the cell identifier to the char buffer.
  * This is useful both for struct gsm0808_cell_id and struct gsm0808_cell_id_list2.
  * See also gsm0808_cell_id_name() and gsm0808_cell_id_list_name().
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index a518b28..1ff1286 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -157,6 +157,7 @@
 gsm0808_bssmap_name;
 gsm0808_cause_name;
 gsm0808_cause_class_name;
+gsm0808_get_cause;
 gsm0808_create_ass;
 gsm0808_create_ass2;
 gsm0808_create_assignment_completed;