libnl: add ptest support

All tests are installed, but only what `make check`
runs is run, so currently that's 1 test named `check-all`

`libcheck` needs to be present for ./configure to generate
the check* tests.

An issue asking about upstream testing strategy is opened at
https://github.com/thom311/libnl/issues/270

(From OE-Core rev: 23a785a373f76a24f4f7dd867522ce296cbf30f3)

Signed-off-by: Yi Fan Yu <yifan.yu@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-support/libnl/files/enable-serial-tests.patch

@@ -0,0 +1,28 @@
+From b1476d89bf7a0bc6062438731ee4e9026696328b Mon Sep 17 00:00:00 2001
+From: Eric Xu <chi.xu@windriver.com>
+Date: Fri, 9 Mar 2018 03:38:49 +0000
+Subject: [PATCH] Add ptest for libnl
+
+serial-tests is required to generate those targets.
+
+Signed-off-by: Eric Xu <chi.xu@windriver.com>
+---
+ configure.ac | 2 +-
+ 1 files changed, 1 insertion(+), 1 deletions(-)
+
+diff --git a/configure.ac b/configure.ac
+index dfead98..2cc8257 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -46,7 +46,7 @@ AC_INIT(libnl, [libnl_version], [], [], [http://www.infradead.org/~tgr/libnl/])
+ AC_CONFIG_HEADERS([lib/defs.h])
+ AC_CONFIG_AUX_DIR([build-aux])
+ AC_CONFIG_MACRO_DIR([m4])
+-AM_INIT_AUTOMAKE([-Wall foreign subdir-objects])
++AM_INIT_AUTOMAKE([-Wall foreign subdir-objects serial-tests])
+ m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES(yes)], [])
+ m4_ifdef([AM_PROG_AR], [AM_PROG_AR])
+ 
+-- 
+2.13.3
+