qcacmn: Add qdf_slist

For memory savings it is sometimes desirable to use a single-linked list
instead of a double-linked list. However, the Linux kernel does not
provide a default implementation of a single-linked list.

Add a very simple single-linked list implementation to WLAN for general
use.

Change-Id: I2959f34649a0d8e0b312d9d67c81de17753b9b6c
CRs-Fixed: 2418493

qdf/test/qdf_slist_test.h

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2019 The Linux Foundation. All rights reserved.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for
+ * any purpose with or without fee is hereby granted, provided that the
+ * above copyright notice and this permission notice appear in all
+ * copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+ * WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+ * AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+ * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
+ * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+ * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef __QDF_SLIST_TEST_H
+#define __QDF_SLIST_TEST_H
+
+#ifdef WLAN_SLIST_TEST
+/**
+ * qdf_slist_unit_test() - run the qdf slist unit test suite
+ *
+ * Return: number of failed test cases
+ */
+uint32_t qdf_slist_unit_test(void);
+#else
+static inline uint32_t qdf_slist_unit_test(void)
+{
+	return 0;
+}
+#endif /* WLAN_SLIST_TEST */
+
+#endif /* __QDF_SLIST_TEST_H */
+