Update the xburst target to kernel version 3.18 and also remove the broken 3.10 support. Signed-off-by: Lars-Peter Clausen <lars@metafoo.de> git-svn-id: svn://svn.openwrt.org/openwrt/trunk@45031 3c298f89-4303-0410-b956-a3cf2f4a3e73