res/res_format_attr_silk: Expose format attributes to other modules

This patch adds the .get callback to the format attribute module, such
that the Asterisk core or other third party modules can query for the
negotiated format attributes.

Change-Id: Ia24f55cf9b661d651ce89b4f4b023d921380f19c

res/res_format_attr_silk.c

@@ -200,12 +200,36 @@ static struct ast_format *silk_set(const struct ast_format *format, const char *
 	return cloned;
 }
 
+static const void *silk_get(const struct ast_format *format, const char *name)
+{
+	struct silk_attr *attr = ast_format_get_attribute_data(format);
+	unsigned int *val;
+
+	if (!strcasecmp(name, "sample_rate")) {
+		val = &attr->samplerate;
+	} else if (!strcasecmp(name, "max_bitrate")) {
+		val = &attr->maxbitrate;
+	} else if (!strcasecmp(name, "dtx")) {
+		val = &attr->dtx;
+	} else if (!strcasecmp(name, "fec")) {
+		val = &attr->fec;
+	} else if (!strcasecmp(name, "packetloss_percentage")) {
+		val = &attr->packetloss_percentage;
+	} else {
+		ast_log(LOG_WARNING, "unknown attribute type %s\n", name);
+		return NULL;
+	}
+
+	return val;
+}
+
 static struct ast_format_interface silk_interface = {
 	.format_destroy = silk_destroy,
 	.format_clone = silk_clone,
 	.format_cmp = silk_cmp,
 	.format_get_joint = silk_getjoint,
 	.format_attribute_set = silk_set,
+	.format_attribute_get = silk_get,
 	.format_parse_sdp_fmtp = silk_parse_sdp_fmtp,
 	.format_generate_sdp_fmtp = silk_generate_sdp_fmtp,
 };