misc: unify pcap rx / tx / drop trace

Use a single vnet_pcap_t in vlib_global_main, specifically to support
unified tracing

Update sphinx docs, doxygen tags

Type: refactor
Ticket: VPP-1776

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: Id15d41a596712968c0714cef1bd2cd5bc9cbdd55
diff --git a/src/vnet/interface.h b/src/vnet/interface.h
index 0c273c6..00ed1f0 100644
--- a/src/vnet/interface.h
+++ b/src/vnet/interface.h
@@ -843,12 +843,11 @@
 
   vnet_hw_interface_nodes_t *deleted_hw_interface_nodes;
 
-  /* pcap drop tracing */
-  int drop_pcap_enable;
-  pcap_main_t pcap_main;
-  u8 *pcap_filename;
-  u32 pcap_sw_if_index;
-  u32 pcap_pkts_to_capture;
+  /*
+   * pcap drop tracing
+   * Only the drop filter hash lives here. See ../src/vlib/main.h for
+   * the rest of the variables.
+   */
   uword *pcap_drop_filter_hash;
 
   /* Buffer metadata format helper functions */
@@ -899,7 +898,10 @@
   int enable;
   int status;
   u32 packets_to_capture;
-  vlib_rx_or_tx_t rxtx;
+  u32 max_bytes_per_pkt;
+  u8 rx_enable;
+  u8 tx_enable;
+  u8 drop_enable;
   u32 sw_if_index;
   int filter;
 } vnet_pcap_dispatch_trace_args_t;