VPP-118: add support for variable length arrays to jvpp

* extends VPP's message definition language with the following syntax:

u32 count:
u8 array[count];

which is traslated to:

u32 count;
u8 array[0];

but now, python API representation generated by vppapigen
contains information about where the array length is stored.

* modifies existing response messages to use the new syntax

Change-Id: I68210bc7a3a755d03d067e9b79a567f40e2d31f3
Signed-off-by: Marek Gradzki <mgradzki@cisco.com>
diff --git a/vppapigen/gram.y b/vppapigen/gram.y
index 09e2006..ccdcc8f 100644
--- a/vppapigen/gram.y
+++ b/vppapigen/gram.y
@@ -31,6 +31,7 @@
  YYSTYPE add_union(YYSTYPE, YYSTYPE);
  YYSTYPE add_scalar_vbl(YYSTYPE);
  YYSTYPE add_vector_vbl(YYSTYPE, YYSTYPE);
+ YYSTYPE add_variable_length_vector_vbl(YYSTYPE, YYSTYPE);
  YYSTYPE set_flags(YYSTYPE, YYSTYPE);
 %}
 
@@ -86,4 +87,5 @@
 
 vbl:      NAME                      {$$ = add_scalar_vbl($1);}
         | NAME LBRACK NUMBER RBRACK {$$ = add_vector_vbl($1, $3);}
+        | NAME LBRACK NAME RBRACK {$$ = add_variable_length_vector_vbl($1, $3);}
           ;