misc: add callback hooks and refactor pmc

Callbacks for monitoring and performance measurement:
- Add new callback list type, with context
- Add callbacks for API, CLI, and barrier sync
- Modify node dispatch callback to pass plugin-specific context
- Modify perfmon plugin to keep PMC samples local to the plugin
- Include process nodes in dispatch callback
- Pass dispatch function return value to callback

Type: refactor

Signed-off-by: Tom Seidenberg <tseidenb@cisco.com>
Change-Id: I28b06c58490611e08d76ff5b01b2347ba2109b22

src/vlib/node.h

@@ -235,9 +235,6 @@ typedef struct
   u64 calls, vectors, clocks, suspends;
   u64 max_clock;
   u64 max_clock_n;
-  u64 perf_counter0_ticks;
-  u64 perf_counter1_ticks;
-  u64 perf_counter_vectors;
 } vlib_node_stats_t;
 
 #define foreach_vlib_node_state					\
@@ -484,10 +481,6 @@ typedef struct vlib_node_runtime_t
   u32 vectors_since_last_overflow;	/**< Number of vector elements
 					  processed by this node. */
 
-  u32 perf_counter0_ticks_since_last_overflow; /**< Perf counter 0 ticks */
-  u32 perf_counter1_ticks_since_last_overflow; /**< Perf counter 1 ticks */
-  u32 perf_counter_vectors_since_last_overflow;	/**< Perf counter vectors */
-
   u32 next_frame_index;			/**< Start of next frames for this
 					  node. */