Linux-2.6.33 compat, .ctl_name removed from struct ctl_table

As of linux-2.6.33 the ctl_name member of the ctl_table struct
has been entirely removed.  The upstream code has been updated
to depend entirely on the the procname member.  To handle this
all references to ctl_name are wrapped in a CTL_NAME macro which
simply expands to nothing for newer kernels.  Older kernels are
supported by having it expand to .ctl_name = X just as before.

config/spl-build.m4

@@ -36,6 +36,7 @@ AC_DEFUN([SPL_AC_CONFIG_KERNEL], [
 	SPL_AC_PATH_IN_NAMEIDATA
 	SPL_AC_TASK_CURR
 	SPL_AC_CTL_UNNUMBERED
+	SPL_AC_CTL_NAME
 	SPL_AC_FLS64
 	SPL_AC_DEVICE_CREATE
 	SPL_AC_5ARGS_DEVICE_CREATE
@@ -641,6 +642,25 @@ AC_DEFUN([SPL_AC_CTL_UNNUMBERED],
 	])
 ])
 
+dnl #
+dnl # 2.6.33 API change,
+dnl # Removed .ctl_name from struct ctl_table.
+dnl #
+AC_DEFUN([SPL_AC_CTL_NAME], [
+	AC_MSG_CHECKING([whether struct ctl_table has ctl_name])
+	SPL_LINUX_TRY_COMPILE([
+		#include <linux/sysctl.h>
+	],[
+		struct ctl_table ctl;
+		ctl.ctl_name = 0;
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_CTL_NAME, 1, [struct ctl_table has ctl_name])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
 dnl #
 dnl # 2.6.16 API change.
 dnl # Check if 'fls64()' is available