core: add helper function for flag reset

- add helper function for flag reset (needed for bugfix in #GH1674)
- patch from: Julien Chavanton jchavanton at gmail dot com

src/core/flags.c

@@ -52,6 +52,11 @@ int resetflag( struct sip_msg* msg, flag_t flag ) {
 	return 1;
 }
 
+int resetflags( struct sip_msg* msg, flag_t flags ) {
+	msg->flags &= ~ flags;
+	return 1;
+}
+
 int isflagset( struct sip_msg* msg, flag_t flag ) {
 	return (msg->flags & (1<<flag)) ? 1 : -1;
 }

src/core/flags.h

@@ -44,6 +44,7 @@ struct sip_msg;
 
 int setflag( struct sip_msg* msg, flag_t flag );
 int resetflag( struct sip_msg* msg, flag_t flag );
+int resetflags( struct sip_msg* msg, flag_t flags );
 int isflagset( struct sip_msg* msg, flag_t flag );