Fix const string return values so that wrapper generators know that these...

Fix const string return values so that wrapper generators know that these strings do not need to be dealloced.

coreapi/content.c

@@ -115,7 +115,7 @@ void linphone_content_set_buffer(LinphoneContent *content, const void *buffer, s
 	((char *)content->lcp.data)[size] = '\0';
 }
 
-char * linphone_content_get_string_buffer(const LinphoneContent *content) {
+const char * linphone_content_get_string_buffer(const LinphoneContent *content) {
 	return (char *)content->lcp.data;
 }
 

coreapi/content.h

@@ -165,7 +165,7 @@ LINPHONE_PUBLIC void linphone_content_set_buffer(LinphoneContent *content, const
  * @param[in] content LinphoneContent object
  * @return The string content data buffer.
  */
-LINPHONE_PUBLIC char * linphone_content_get_string_buffer(const LinphoneContent *content);
+LINPHONE_PUBLIC const char * linphone_content_get_string_buffer(const LinphoneContent *content);
 
 /**
  * Set the string content data buffer.

coreapi/linphonecore.c

@@ -7074,7 +7074,7 @@ int linphone_payload_type_get_normal_bitrate(const LinphonePayloadType *pt) {
 	return pt->normal_bitrate;
 }
 
-char * linphone_payload_type_get_mime_type(const LinphonePayloadType *pt) {
+const char * linphone_payload_type_get_mime_type(const LinphonePayloadType *pt) {
 	return pt->mime_type;
 }
 

coreapi/linphonecore.h

@@ -257,7 +257,7 @@ LINPHONE_PUBLIC int linphone_payload_type_get_normal_bitrate(const LinphonePaylo
  * @param[in] pt LinphonePayloadType object
  * @return The mime type.
  */
-LINPHONE_PUBLIC char * linphone_payload_type_get_mime_type(const LinphonePayloadType *pt);
+LINPHONE_PUBLIC const char * linphone_payload_type_get_mime_type(const LinphonePayloadType *pt);
 
 /**
  * Get the number of channels.