buildroot

lftp: bump version to 4.6.1

-Bump version to 4.6.1
-Add a hash file
-Use xz tarball to save space and bandwidth

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>