add mactime plugin unit / code coverage tests

The unit and code coverage tests are boring. The rest of the patch
involves test and packet-generator infra cleanups.

Teach the "make test-xxx" family of targets to set the api test plugin
path correctly, to make "binary-api <api-message-name> <args>" debug
CLI commands work correctly in the "make test"
environment. Unfortunately involves both the top-level and test
Makefiles.

Add a minor pg cli feature, a CLI to manually set
s->sw_if_index[VLIB_TX].

Consider the case where one configures an interface with both a
device-input and an output feature. To test the output feature using
the pg, it's necessary to inject packets into the interface output
node with both b->sw_if_index[VLIB_TX] and b->sw_if_index[VLIB_RX] set
correctly. For example:

packet-generator new {
 name tx
 limit 15
 size 128-128
 interface local0  # rx: device input feature not configured on local0
 tx-interface loop0 # tx: output node requires b->sw_if_index[VLIB_TX]
 node loop0-output
 data {
   hex 0x01005e7ffffa000dead0000008000102030405060708090a0b0c0d0e0f0102030405
   }
}

Fix a longstanding bug in the packet generator stream setup.  Remove
kludges which set b->sw_if_index[VLIB_TX] to ~0 [in multiple places]
instead of using the stream value s->sw_if_index[VLIB_TX], and setting
THAT datum correctly.

Change-Id: I1097a18e8db73661ded6b822c1d718f7e5cf36ed
Signed-off-by: Dave Barach <dave@barachs.net>
diff --git a/src/vnet/pg/input.c b/src/vnet/pg/input.c
index 39f0692..7171bbd 100644
--- a/src/vnet/pg/input.c
+++ b/src/vnet/pg/input.c
@@ -1108,7 +1108,7 @@
 	vnet_buffer (b1)->sw_if_index[VLIB_RX] = s->sw_if_index[VLIB_RX];
 
       vnet_buffer (b0)->sw_if_index[VLIB_TX] =
-	vnet_buffer (b1)->sw_if_index[VLIB_TX] = (u32) ~ 0;
+	vnet_buffer (b1)->sw_if_index[VLIB_TX] = s->sw_if_index[VLIB_TX];
 
       if (set_data)
 	{
@@ -1133,8 +1133,7 @@
 
       b0 = vlib_get_buffer (vm, bi0);
       vnet_buffer (b0)->sw_if_index[VLIB_RX] = s->sw_if_index[VLIB_RX];
-      /* s->sw_if_index[VLIB_TX]; */
-      vnet_buffer (b0)->sw_if_index[VLIB_TX] = (u32) ~ 0;
+      vnet_buffer (b0)->sw_if_index[VLIB_TX] = s->sw_if_index[VLIB_TX];
 
       if (set_data)
 	clib_memcpy_fast (b0->data, data, n_data);
@@ -1266,7 +1265,7 @@
 	  b = vlib_get_buffer (vm, buffers[current_buffer_index]);
 	  clib_memcpy_fast (b->data, d0 + data_offset, bytes_this_chunk);
 	  vnet_buffer (b)->sw_if_index[VLIB_RX] = s->sw_if_index[VLIB_RX];
-	  vnet_buffer (b)->sw_if_index[VLIB_TX] = (u32) ~ 0;
+	  vnet_buffer (b)->sw_if_index[VLIB_TX] = s->sw_if_index[VLIB_TX];
 	  b->flags = 0;
 	  b->next_buffer = 0;
 	  b->current_data = 0;