queue: add requeue, fix unqueue_matching

Synchronized with emane.git's implementation of this code which
includes a unit test.

This commit also fixes two bugs in unqueue_matching and one inb
unqueue:

- unqueue_matching was returning the wrong pointer when
  there was no match

- both unqueue_matching and unqueue were not clearing the vacated
  queue entry after removing the item

openair2/PHY_INTERFACE/queue_test_run

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+opts=(
+    -Wall -Werror
+    -Wno-error=int-to-pointer-cast
+    -Wno-int-to-pointer-cast
+    -DUNITTEST
+)
+
+set -x
+
+gcc "${opts[@]}" -fsanitize=address -o queue_test queue_test.c queue.c || exit
+./queue_test || exit
+
+gcc "${opts[@]}" -o queue_test queue_test.c queue.c || exit
+valgrind ./queue_test || exit
+
+: PASS