xinetd: change download location

xinetd.org is down, change to github instead.
Hash can not be used, the tarball is generated.

Signed-off-by: Karoly Kasza <kaszak@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>