misc: classifier-based packet trace filter

See .../src/vnet/classify/trace_classify.h for the business end
of the scheme.

It would be best to hash pkts, prefetch buckets, and do the primary
table lookups two at a time. The inline as given works, but perf
tuning will be required. "At least it works..."

Add "classify filter" debug cli, for example:
classify filter mask l3 ip4 src dst \
  match l3 ip4 dst 192.168.2.10 src 192.168.1.10

Add "pcap rx | tx trace ... filter" to use the current classify filter chain

Patch includes sphinx documentation and doxygen tags.

Next step: device-driver integration

Type: feature

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: I05b1358a769f61e6d32470e0c87058f640486b26
diff --git a/src/vnet/CMakeLists.txt b/src/vnet/CMakeLists.txt
index 2a78381..1e51f3d 100644
--- a/src/vnet/CMakeLists.txt
+++ b/src/vnet/CMakeLists.txt
@@ -384,6 +384,7 @@
 ##############################################################################
 list(APPEND VNET_SOURCES
   classify/vnet_classify.c
+  classify/trace_classify.h
   classify/ip_classify.c
   classify/in_out_acl.c
   classify/policer_classify.c
@@ -400,6 +401,7 @@
 
 list(APPEND VNET_HEADERS
   classify/vnet_classify.h
+  classify/trace_classify.h
   classify/in_out_acl.h
   classify/policer_classify.h
   classify/flow_classify.h