sdlog2: add logbuffer_reset to reset pointers

This allows resetting of the logbuffer without having to free and malloc
again.

src/modules/sdlog2/logbuffer.c

@@ -156,3 +156,10 @@ void logbuffer_free(struct logbuffer_s *lb)
 		perf_free(lb->perf_dropped);
 	}
 }
+
+void logbuffer_reset(struct logbuffer_s *lb)
+{
+	// Keep the buffer but reset the pointers.
+	lb->write_ptr = 0;
+	lb->read_ptr = 0;
+}

src/modules/sdlog2/logbuffer.h

@@ -69,4 +69,6 @@ void logbuffer_mark_read(struct logbuffer_s *lb, int n);
 
 void logbuffer_free(struct logbuffer_s *lb);
 
+void logbuffer_reset(struct logbuffer_s *lb);
+
 #endif