misc: clean up "pcap [rx|tx] trace" debug CLI

Separate debug CLI arg parsing from the underlying action
function. Fixes a number of subtle ordering dependencies, and will
allow us to add a binary API to control the feature at some point in
the future.

Type: refactor
Ticket: VPP-1770

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: Id0dbeda06dad20e756c941c691e2088ce3c50ec7
diff --git a/src/vnet/interface.h b/src/vnet/interface.h
index e6418f9..42aada4 100644
--- a/src/vnet/interface.h
+++ b/src/vnet/interface.h
@@ -893,6 +893,18 @@
 void vnet_register_format_buffer_opaque2_helper
   (vnet_buffer_opquae_formatter_t fn);
 
+typedef struct
+{
+  u8 *filename;
+  int enable;
+  int status;
+  u32 packets_to_capture;
+  vlib_rx_or_tx_t rxtx;
+  u32 sw_if_index;
+} vnet_pcap_dispatch_trace_args_t;
+
+int vnet_pcap_dispatch_trace_configure (vnet_pcap_dispatch_trace_args_t *);
+
 #endif /* included_vnet_interface_h */
 
 /*