alpine: update to 2.11

Update Alpine to 2.11. Also switch to use .tar.xz package.

Signed-off-by: Antti Seppälä <a.seppala@gmail.com>


git-svn-id: svn://svn.openwrt.org/openwrt/packages@39551 3c298f89-4303-0410-b956-a3cf2f4a3e73