xbps-src: reserve "kernel_hooks_version" variable.

This variable can be used in templates to specify the kernel version
passed to the Vanilla kernel hooks in /etc/kernel.d/<target>.

xbps-src/shutils/metadata.sh

@@ -47,7 +47,7 @@ xbps_write_metadata_pkg()
 			preserve keep_empty_dirs xml_entries sgml_entries \
 			xml_catalogs sgml_catalogs gconf_entries gconf_schemas \
 			gtk_iconcache_dirs font_dirs dkms_modules provides \
-			conflicts
+			kernel_hooks_version conflicts
 		. $XBPS_SRCPKGDIR/${sourcepkg}/${subpkg}.template
 		pkgname=${subpkg}
 		set_tmpl_common_vars

xbps-src/shutils/metadata_scripts.sh

@@ -76,6 +76,14 @@ UPDATE="\$4"
 #
 _EOF
 
+	#
+	# Handle kernel hooks.
+	#
+	if [ -n "${kernel_hooks_version}" ]; then
+		_add_trigger kernel
+		echo "export kernel_hooks_version=\"${kernel_hooks_version}\"" >> $tmpf
+	fi
+
 	#
 	# Handle DKMS modules.
 	#

xbps-src/shutils/tmpl_funcs.sh.in

@@ -105,7 +105,7 @@ reset_tmpl_vars()
 			ignore_vdeps_dir noverifyrdeps conflicts dkms_modules \
 			gconf_entries gconf_schemas stow_copy stow_copy_files \
 			pre_remove post_remove post_stow do_build do_install \
-			homepage license \
+			homepage license kernel_hooks_version \
 			XBPS_EXTRACT_DONE XBPS_CONFIGURE_DONE \
 			XBPS_BUILD_DONE XBPS_INSTALL_DONE FILESDIR DESTDIR \
 			SRCPKGDESTDIR PATCHESDIR CFLAGS CXXFLAGS CPPFLAGS \