Improve fifo allocator performance

- add option to preallocate fifos in a segment
- track active fifos with doubly linked list instead of vector
- update udp redirect test code to read fifo pointers from API call
  instead of digging them up from fifo segment header
- input-node based active-open session generator

Change-Id: I804b81e99d95f8690d17e12660c6645995e28a9a
Signed-off-by: Dave Barach <dave@barachs.net>
Signed-off-by: Florin Coras <fcoras@cisco.com>
Signed-off-by: Dave Barach <dbarach@cisco.com>

src/vlibapi/api.h

@@ -193,6 +193,9 @@ typedef struct
 
   i32 vlib_signal;
 
+  /* vlib input queue length */
+  u32 vlib_input_queue_length;
+
   /* client side message index hash table */
   uword *msg_index_by_name_and_crc;