vapi: remove directory name from include guards

Script vapi_c_gen.py uses full paths to source files to generate include
guards in files with `.vapi.h` extension. This makes the content of
header files depend on build directory which causes reproducibility
issues (cannot get identical build output when building in a different
directory).

Commit 4c64b6edc86f7 fixes this for .hpp files, but seems to forget
about .h files. Use its fix for these as well.

Type: fix
Change-Id: Ida638c7b4630fac1f6d968a9203a409648bef55c
Signed-off-by: Oleksandr Hnatiuk <ohnatiuk@cisco.com>

src/vpp-api/vapi/vapi_c_gen.py

@@ -891,7 +891,7 @@ def gen_json_unified_header(parser, logger, j, io, name):
     orig_stdout = sys.stdout
     sys.stdout = io
     include_guard = "__included_%s" % (
-        j.replace(".", "_")
+        f.replace(".", "_")
         .replace("/", "_")
         .replace("-", "_")
         .replace("+", "_")