odhcp6c: bump to git HEAD version

5d6fec3 Merge pull request #50 from sartura/libubox_md5_reuse
33a2ba1 odhcp6c: reuse md5 from libubox

Switch PKG_SOURCE_URL to git.lede-project.org/project/odhcp6c.git

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>