Replace --disable-libv4l2 with --disable-v4l2

This disables V4L2 completely.

configure.ac

@@ -1803,22 +1803,22 @@ fi
 dnl
 dnl  Video4Linux 2
 dnl
-AC_ARG_ENABLE(libv4l2, [AS_HELP_STRING([--disable-libv4l2],
-  [disable userspace V4L2 library (default auto)])])
+AC_ARG_ENABLE(v4l2, [AS_HELP_STRING([--disable-v4l2],
+  [disable Video4Linux version 2 (default auto)])])
 AC_ARG_ENABLE(pvr, [AS_HELP_STRING([--enable-pvr],
   [support PVR V4L2 cards (default disabled)])])
 have_v4l2="no"
-AC_CHECK_HEADERS([linux/videodev2.h sys/videoio.h], [
+AS_IF([test "$enable_v4l2" != "no"], [
+  AC_CHECK_HEADERS([linux/videodev2.h sys/videoio.h], [
     have_v4l2="yes"
+  ])
 ])
 AS_IF([test "$have_v4l2" = "yes"], [
-  AS_IF([test "${enable_libv4l2}" != "no"], [
   PKG_CHECK_MODULES(LIBV4L2, libv4l2, [
     AC_DEFINE(HAVE_LIBV4L2, 1, [Define to 1 if libv4l2 is available])
   ], [
     AC_MSG_WARN([${LIBV4L2_PKG_ERRORS}.])
   ])
-  ])
   AS_IF([test "${enable_pvr}" = "yes"], [
     VLC_ADD_PLUGIN([pvr])
   ])