xl2tpd: add from OE-Classic, update and tidy up

* Update to version 1.3.1
* Fetch source from a git tag as upstream apparently no longer publishes
  release tarballs
* Add virtual/kernel to DEPENDS since it needs the kernel source
* Inherit update-rc.d.bbclass
* Handle hardcoded paths in initscript
* Add LIC_FILES_CHKSUM
* Set SUMMARY (which sets DESCRIPTION)
* Remove some unnecessary cruft

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>