configure: rework libnl detection and fix libnl-2 case (v2)

Rework libnl detection.

PKG_CHECK_MODULES macro appends FOO_CFLAGS and FOO_LIBS flags

Example:
LIBNL_CFLAGS = -I/usr/include/libnl3
LIBNL_LIBS = -lnl-genl-3 -lnl-3

while AC_SEARCH_LIBS only prepends -llibrary to LIBS, so AC_SEARCH_LIBS is not helpful.

Use pkg-config PC file names to search for minimum package versions:
libnl 3.+ -- libnl-3.0.pc
libnl 2.+ -- libnl-2.0.pc
libnl 1.+ -- libnl-1.0.pc

Patch also changes $has_libnl_ver == 0 error message and suppresses failed PKG_CHECK_MODULES output.

Austin pointed out that libnl-2.0 provide only libnl-2.0.pc pkg-config file, while libnl-3 has at least 5 of them (for every `so'). This is why we check libnl-3.0.pc and libnl-genl-3.0.pc in libnl-3 case.

Many thanks to Austin Zhang for help.
v2: Namhyung Kim reported that libnl-1.0.pc on Ubuntu is named libnl-1.pc.

Reported-and-tested-by: Austin Zhang <zhang.austin(a)gmail.com>
Tested-by: Namhyung Kim <namhyung(a)gmail.com>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky(a)gmail.com>

---

  configure.ac | 15 +++++++--------
  1 file changed, 7 insertions(+), 8 deletions(-)

Sergey Senozhatsky

configure.ac +7 -8

index b8c183f..02952b3 100644
@@ -54,15 +54,14 @@ PKG_CHECK_MODULES([PCIUTILS], [libpci],[has_libpci=1],[
 
 
  has_libnl_ver=0
-PKG_CHECK_MODULES([LIBNL], [libnl-3.0 libnl-genl-3.0], [
-	has_libnl_ver=3], [
-	AC_SEARCH_LIBS([nl_socket_alloc], [nl-3 nl-genl-3], [
-		has_libnl_ver=3], [
-		AC_SEARCH_LIBS([nl_socket_alloc], [nl], [
-			has_libnl_ver=2], [
-			PKG_CHECK_MODULES([LIBNL], [libnl-1], [has_libnl_ver=1], [])])])])
+# libnl-2 provides only libnl-2.0.pc file, so we check for separate libnl-genl-3.0.pc
+# pkg-config file just for libnl-3.0 case.
+#
+PKG_CHECK_MODULES([LIBNL], [libnl-3.0 >= 3.0 libnl-genl-3.0 >= 3.0], [has_libnl_ver=3], [
+	PKG_CHECK_MODULES([LIBNL], [libnl-2.0 >= 2.0], [has_libnl_ver=2], [
+		PKG_CHECK_MODULES([LIBNL], [libnl-1], [has_libnl_ver=1], [has_libnl_ver=0])])])
  if (test "$has_libnl_ver" -eq 0); then
-	AC_MSG_ERROR(libnl is required but not found)
+	AC_MSG_ERROR(libnl and libnl-genl are required but were not found)
  fi
  if (test "$has_libnl_ver" -gt 1); then
  	AC_DEFINE([HAVE_LIBNL20], [1], [Define if you have libnl-2.0 or higher])

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